To disinfect something is to clean it so thoroughly that you kill any bacteria that might have been living on it. It's particularly important to disinfect cuts and scratches.
You can disinfect your kitchen counters with cleaning products, or disinfect a scrape by washing it with soap and water. Public swimming pools have chlorine added to their water to disinfect them, and bleach is a good all-purpose chemical used to disinfect floors, laundry, and other things that might be harboring nasty bugs. Infect comes from a Latin root word, inficere, "to spoil or stain." Adding the prefix dis-, "do the opposite of," gives you disinfect.