Other forms: capablest; capabler
To be capable of something is to be able to do it, like your little brother who is perfectly capable of tying his own shoes, but likes having everyone else do it for him.
When people are capable, they can handle whatever task is at hand, like a capable teacher who can explain difficult concepts and make it fun. You may also have heard that someone "isn't capable" of, say, committing a crime or hurting someone's feelings. In this case, not being capable is a compliment — it means you just won't let yourself do something to violate your own standards for behavior.