All knives, especially those that you use on a daily basis, usually chef’s knife, should be sharpened every few weeks, depending on how much you use them.
You can use a knife sharpener (one with 1-2 slots), through which you pass the knife perfectly straight several times, first through the hard slot, then the fine one for polishing. But if you have a very dull knife and you want it to be really sharp, ideally you should use a sharpening stone.
Leave the stone to soak in water for 15 minutes. If your stone is too dry, it can scratch your knife blades, so it’s better to soak it some more in water. The blade needs to be sharpened at a 20 degree angle. Hold the knife handle with one hand and the opposite side of the blade with the other hand, putting pressure on it while you sharpen the knife.
Slide the blade down the stone several times on each side. Sharpen the knife evenly on each side, for example run it over the stone 5 times on each side.