It depends on the blade. If it’s a bare carbon steel blade, clean it off when you’re done using it, and wipe on a thin layer of food grade mineral oil. If it’s coated, you might not have to do much at all other than keep the exposed edge clean and dry. Stainless knives require less work, usually just cleaning. As for keeping them sharp, there are loads of sharpeners and strops available to keep them in good working condition, or, if the manufacturer offers it, you can send it in and they will sharpen and clean it.