The adverb not is used for negation. Do you like drinking cod liver oil? No, I do not like drinking cod liver oil.
Not is a powerful word. When Hamlet says "to be or not to be," he is questioning whether he should live or die, the inverse of living. Just be careful of what's called a "double negative," where you use not with another negating word and end up negating your negation. If you say you don't know nothing about something, that means you do know something. Not is often contracted as in don't, or isn't.