There are several types of cocaine. It can be used alone but is typically mixed with other drugs. Crack cocaine is one example. It is called this because it makes a crackling noise when a user heats it to smoke it.
Other forms exist as well, including speedball, which is an injectable combination of cocaine and heroin linked to several prominent deaths including Chris Farley, Mitch Hedberg, Phillip Seymour Hoffman and River Phoenix. Freebase is a refined hydrochloride salt form of cocaine that is highly dangerous.