Что (pronounced "shto", not "chto") and какой (pronounced "kakoy") both mean "what". As a loose rule, какой means "which". The correct rule is that if a noun follows "what", use какой. If no noun follows "what", use что.

As a memory aid, the following noun's gender and number change какой. Какой precedes masculine nouns, какая precedes feminine nouns, какое precedes neuter nouns, and какие precedes plural nouns. Because что is never followed by a noun, it only changes form in different cases.

If you just want to "get by," always use что for "what."