It is advisable to learn the proper way of re-sharpen blade in order to keep sharp edge. It is recommended to re-sharpen blade regularly: at least a couple of times per month. There are whetstones of 3 different roughness or grits available: coarse, medium, and fine. For home use, a whetstone of medium grit is recommended.
Make an angle of 15 degrees between the blade and whetstone; and maintain the angle throughout the sharpening process. (Placing a 2mm-thick coin between the blade and whetstone at the spine of the blade will help making an angle of 15 degrees.)
Do not wash away thick water, which comes out while sharpening a blade. It works as lubricant and it necessary for sharpening. Same reciprocating movement applies for both one-edged blade and double-edged blade.
When the unsharpened edge of the other side becomes rough, it is the sign that the sharpening of the edged-side is done. Finish it off with sharpening the other side in the same way to smooth the rough edge.