Keep cutting edge of your knife sharp.
There are two main types of steel for knives, carbon and stainless. Generally, carbon steel knives will keep its cutting edge sharp longer. If you take care properly, it can be sharpened every two years. Stainless steel knives need to be sharpened more often as it keeps it edge sharp for shorter period of time.
It’s very important to always cut on softer materials then the hardness of your blade is. Use wood or plastic plate for cutting. Never cut on ceramic, glass or steel plates.
Never put your knives in dishwasher. Knives must always been hand washed if you want to prevent your steel from damage.
Carbon steel knives should be cleaned and dried after every single cutting. It is completely normal that carbon blades change its color after some time. It’s natural oxidation. To keep it in better condition, I recommend to put thin layer of oil on the blade after use.