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. 

Select the grit of the stone. Sharpening stones are available with different grit sizes. For example, you can choose fine, medium and coarse stones. You should use a coarse stone followed by a fine grit if your knives are dull. If your knives have been sharpened recently or they aren't too dull, consider using a medium grit. Try to use a grit level ranging from 325 (for coarse) to 1200 (for extra fine).[3]

The video above, from the How To You YouTube channel, explains everything you need to sharpen with a whetstone at home, and the best methods for doing so. Obviously, you’ll need a whetstone (as well as a few other things), and you’ll want to work near your sink or a bucket so you have easy access to water. Fill a container with water, then soak the whetstone in it until it stops bubbling. Inspect your blades for any trouble spots, and get to sharpening using the methods and motions described in the video; making sure to check your progress as you go. We’ve talked about sharpening knives with whetstones before, but this guide is a bit more thorough and the old video has since been removed.
The type and size of the blade being sharpened determines the size of the stone needed. In general , a 6" stone is considered a small sharpening stone, an 8" stone is a common larger size, and a stone larger than 8" (10"-12" are available) is considered generously sized. Stones smaller than 6" (3" and 4" stones are quite common), are considered pocket stones and can be used for toolboxes, tackle boxes and on-the-go sharpening, but are generally not recommended for regular sharpening jobs.
The DuoSharp Plus stones are nicely sized at 8” long by 2 5/8” wide and have two grits on each stone to maximize value. The Plus in the name refers to an area of continuous grit in the otherwise interrupted grit surface of the stone. This area is for sharpening edges with fine points that might be difficult on the interrupted surface. A coarse/fine DuoSharp Plus stone is a good single stone to start a sharpening toolkit.
Now that you're holding the handle and the blade is in position, gently apply some pressure to the belly of the blade with your left hand fingers – "roughly the amount of pressure to semi depress a sponge," says Warner. Starting at the tip, glide the blade up and down the stone – around five strokes up and down is a good number. Then move to the middle – five more strokes. Finally five strokes up and down on the heel.
Selecting the right sharpening angle is the next step in sharpening. For more detailed instructions on selecting the right angle, try reading this article. Regardless of the method of sharpening, a appropriate angle should be selected. This angle doesn't need to be exact but following some general guidelines is a good idea. Most knife manufacturers recommend a roughly 20 degree angle. Depending on the use of your knife, you can move up or down from that angle. A fillet or slicing knife is never used on anything hard so an angle a few degrees less will produce a sharper edge. On the other hand, a survival knife with various uses can benefit from a more durable edge a few degrees larger.