Choose the style of stone. You'll need to choose a natural or synthetic stone that can be used wet (soaked in water), with oil, or dry. There are also diamond stones that are actually very small diamonds attached to a metal surface. Stones that are soaked in water are softer stones which means you can quickly sharpen your knives. Unfortunately, these stones will wear down faster than the others. Oil stones are the least expensive and they're made of a harder material.[2] 

Different knives are sharpened differently according to grind (edge geometry) and application. For example, surgical scalpels are extremely sharp but fragile, and are generally disposed of, rather than sharpened, after use. Straight razors used for shaving must cut with minimal pressure, and thus must be very sharp with a small angle and often a hollow grind. Typically these are stropped daily or more often. Kitchen knives are less sharp, and generally cut by slicing rather than just pressing, and are steeled daily. At the other extreme, an axe for chopping wood will be less sharp still, and is primarily used to split wood by chopping, not by slicing, and may be reground but will not be sharpened daily. In general, but not always, the harder the material to be cut, the higher (duller) the angle of the edge.
The following are my personal favourites and they are all synthetic stones, I do have experience with natural what stones but lets keep it simple, lets stick to synthetic water stones. Believe me, some of the world sharpest knives are sharpened solely on synthetic stones. Here are my personal favourites, I use these water stones every day and the order is not necessarily in priority, they are all good.

Ease of use – Most people in search of a mechanical sharpener want one because they don’t want to be bothered with trying to achieve a perfect edge themselves using a stick or sharpening stone. They want predictable, first class results every time. In that case it’s important that the electric powered device is easy to use, achieves results quickly and with little effort and is designed with user safety in mind. Keep in mind too that it’s easy to apply too much pressure when using a mechanical sharpener and when that happens you’re likely to see unsatisfactory results. In addition there are subtle differences between mechanical devices designed for Asian-style knives and those designed for Western-style knives. This has to do with the sharpening angle discussed above. Don’t get an Asian sharpener if you don’t need precise control over your cuts.
Once you've sharpened one side, you need to flip over, but don't swap the hand gripping the blade – think of it a bit like going backhand with a tennis racket (see above). Lead with the heel this time, rather then with the blade, but repeat the process in three parts. After five strokes on each third of the blade, it's time to check your knife. It's not an exact science, and it all depends on how blunt your blade was to start with (mine was very blunt indeed). But if you sharpen fairly regularly, it should just take a few strokes. 
Why, then, do so many of us shy away from the task? To put it bluntly, it's because it's a rather daunting process for the beginner. Your image of knife sharpening may consist of a hyper-masculine chef slashing away violently at a steel rod (we're looking at you, Gordon). Conversely, you might have seen cooks meticulously and methodically stroking their blade up and down a Japanese waterstone with more intricate attention to detail than a Flemish landscape. 
if you have regular kitchen knives it will not work- first its to deep and the blade does not stick out, not dinner knives but cooking knives. of all the knives i put in it only 1 was wide enough to stick out. the device does not hold the blades. all the blades tested fell out of it, even a hunting knife, maybe its for 1 type of knife and they are selling it as the must have tool for all.. that said sell something useless for a few bucks that most cant use, they got a few bucks that most will blow off and not worry about a refund.. DONT WASTE YOUR MONEY.

But it's a different type of sharp, according to Joe Authbert, product development manager at ProCook. "What it does is add tiny little micro-serrations onto the edge of the blade." But fear not - your smart knife won't end up looking like a bread knife, as you'll be hard-pressed to spot the serrations. "If you looked at it under a microscope, on the cutting edge, there are these little lines that generate the sharpness, rather than a waterstone which is a smooth sharp edge," says Authbert. 
You must put the knife blade's position at the perfect angle which is called "against the stone." What's important is the blade should be facing opposite from you. Where you've determined where the bevel angle is located, then this is what you will position against the stone. It's a good idea to know the differences between various angles for certain blade uses. There's a certain height of the blade that it should be from the stone. You'll be able to find various charts on height of the blade online. Normally, for a pocket knife or kitchen knife, it'll be 17° - 22° angle against the stone. The "Rule of thumb" is the smaller the angle, the sharper the knife. Most makers will have it in the instruction or on their official website.
Your task as a sharpener is to remove that fatigued metal and expose the steel underneath, the fresh strong steel and bring side A and B of the knife together at the Apex precisely, sounds easy doesn’t it? Like peeling a layer off and having a fresh start, over and over. Of course there is much more to it than this but in very basic terms, you want the abrasive properties of the water stone to abrade the fatigued metal away, like an eraser.
Your primary goal is just to improve the edge, make it a little bit sharper. Manage you’re expectations and don’t worry about getting the knife ready for eye surgery on day one. Ignore all those YouTube videos where you see folks performing miracles with their knives, forget that completely. You just want to make the knife a little less dull and by doing so you will achieve what most people will never even attempt. You want to get a taste of sharpening success and it can happen quickly. If you are reading this, or any other cool sharpening tips, you’re on the right path.
For instance, American Novaculite (aka Washita and Arkansas Stones) is a form of metamorphic Chert that produces some of the best known and best loved natural whetstones in existence. Then, there is a form of Belgian Coticule which has been known for providing extra-keen edges since Roman times and, there is a Japanese Siliciclastic sedimentary stone (aka Japanese Water Stones) which consist of a fine silicate particles suspended in a clay matrix. Plus, there are also various types of man-made whetstones available such as Silicon Carbide (aka Crystalon) stones and Aluminum Oxide (aka India Stones) as well as a synthetic Corundum (aka Ruby) rod and Aluminum Oxide impregnated ceramic rods as well as several different types of diamond hones.
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One of the combinations of stones that I was introduced to several years ago is a unique one, it is a 500, 2,000 and 16,000 grit combination. I was apprehensive when I first tried this, that was thousands of knives ago, it works, it is fantastic combination. It is unique because the traditional way of thinking is that we should be doubling the grit sizes as we sharpen, for example, a 500 grit stone should be followed by a 1,000 grit, then 2,000 grit. This line of thought is meant to be flexible, it is a general rule only, I have broken it countless times.
As you apply pressure in one direction you release pressure in the opposite direction. So apply pressure with your finger tips as you push the knife from one end of the stone to the other and release as you pull it back. You could actually lift the knife off of the stone but don’t do this, keep that angle stable. Sharpening becomes this repetitive motion with the first step being the raising of the burr on both sides of the knife from heel to tip.
Actually, the company contacted me to make sure I received the stones and that I was happy with them. Excellent service. The stones are great! I'm pretty much a novice so the clear instructions that came with the stones and the eBook instructions were wonderful. The eBook had quality pictures demonstrating the use of the stones and the written instructions were clear and to the point. Within minutes of opening the box I had the stones figured out and sharpening my AF survival knife, my pocket knife and a couple of my wife's kitchen knives...which included a very expensive chef's knife. Very satisfied with this product and highly recommend it.
Dull knives aren't just annoying — they can be downright dangerous. Keep yours in top shape with the Sharp Pebble Knife Sharpening Stone. It has a #1000 grit side for dealing with dull edges, and a #6000 side for honing to razor-like sharpness. It sits inside a silicone base, inside a non-slip bamboo base, and comes with an angle guide that slides over the spine, ensuring that even beginners can set a proper edge.
Manufacturer contacted and sent a new one for replacement. Great customer service but replacement item was nicked on the corner. It was still usable so i didn't bother to ask for another replacement. I would recommend item to be shipped in another box instead of an over-sized yellow envelop which is not adequate protection. Item sharpen my knife pretty good though..

Understanding Grit: You’ll see a bunch of numbers being thrown around when discussing the grit of a sharpening stone. The number refers to the size of the grit. The larger the number, the finer the grit. A good beginner stone would be a two-sided stone with #400 and #1000 grit. The #400 grit is the courser stone for working out the nicks and imperfections, the #1000 grit is for refining.
Last, it should be noted that dual-sided Coticule/Belgian Blue whetstones are also sometimes available which have a layer of Belgian Blue stone on one side and a layer of Coticule on the other. Thus, these whetstones provide a softer, more coarse, grit on one side and a harder, finer, grit on the other. Plus, due to the inherent toughness of the Belgian Blue stone, these dual-sided stones do not require a substrate layer.
This 600/1,000 grit is my second Unimi knife sharpener, the first is 2,000/6,000 grit and I love them both. Both stones together produce very sharp and well polished knives that reduce the cutting effort and save time in the kitchen. I particularly appreciate that the manufacture printed the grit number on the side of each stone - that helps use the different grits in the proper sequence from the coarser to the finer. The stone comes with a non-slip silicone/rubber base which is very handy.