Bu is the word used as a negation in Mandarin Chinese. It can be added to verbs (as in "bu shi": "not is") or to adjectives (as in "bu hong": "not red"). Or it can be used by itself, much as we would use the word "no".
AFAIK, the only word that is not negated by bu is you, meaning "to have", which has its own negation, mei.
A common way to ask a question in Mandarin is to use a verb and then use the negation of that verb immediatly after. For example : "renshi bu renshi" means "you know not you know" or "Do you know or don't you know?"