http://www.thegooddrugsguide.com/cocaine/faq.htm
» What is freebasing?
Preparing pure cocaine ("base") for injecting or smoking, usually by dissolving and drawing out the impurities with a strong alkali. Freebasing is pretty dangerous as the chemicals involved are highly explosive and the process requires a lot of skill and specific equipment. Crack cocaine is a form of freebase.
» What is crack cocaine?
"Crack cocaine" is a mix of cocaine and baking powder (sodium bicarbonate) which comes as small lumps or 'rocks'. When smoked, the cocaine vapours reach the brain much quicker than snorting, producing an intense but short-lived euphoric rush and - very quickly - a compelling desire for more. Crack is also very harsh on the lungs.
Crack is highly addictive but one hit will not make you addicted.