I have been both a boy scout and worked in a meat department for eight years. This qualifies me to explain how to sharpen a knife. This is caveman 101.
Keep in mind you don’t sharpen serrated knives or ceramic knives. It could break or dull them if you tried. You also don’t sharpen flatware unless you are in prison. This guide applies to regular steel cutting knives.
The easiest way is to use a “Steel”. It might have a better name but that is what we called them in the meat department. A Steel is a short metal rod used for straightening the blade. You might have come across this item in a knife set. You use it by sliding the knife blade up and down it at a low angle. Use the same angle each time. Pretend you are cutting the Steel with the knife. You flip the knife over each time to do both sides. The edge of the knife is thin and this aligns it. If you don’t have a Steel you can also use the back of another straight knife.
Another way is with one or more sharpening stones. Here again, you are straightening the blade. You are also forming it. Some metal is coming off and you could ruin the blade. You take the knife at the same low angle and slide it back and forth across the stone. In the meat department we had three stones of increasing grit. We started on the coarsest and finished on the smoothest grit, leaving a sharp blade.
A final way is with a grinder. We had this in the meat department and always sharpened the knives of customers who asked. The grinder has rotating stone or sandwich the blade between two rotating stones with varying coarseness.
We used all these methods in the meat department. The main tool was the Steel. What you cut determines how your knife dulls. Soft pork loin, no problem. Cutting the meat off a bone will knick up the blade. You won’t have this wear and tear at home. Most of the old meat cutters would sharpen their knives on the stones at night. It gave a better edge than the grinder.
Of these methods, I recommend using the back of another knife if you don’t have a Steel. You will be surprised with the results. I would only use a sharpening stone occasionally if the Steel didn’t work. Finally, ask your local butcher if he will sharpen your knives. If he does that once a year you will be able to keep the edge yourself.