Pretty much like "no" and "not" in English
"Nicht" ist used to negate a verb and "kein" to give a sentence that uses a positive verb a negative meaning. That can often result in the same thing.
She likes to wear no dresses. -> Sie mag es, keine Kleider zu tragen.
She doesn't like wearing dresses. -> Sie mag es nicht, Kleider zu tragen.
Meaning is the same. It's just made differently