When you look up the word on dictionary.com, it states a definition: Nonstandard except in some dialects . am not; are not; is not. It also notes: As a substitute for am not, is not, and are not in declarative sentences, ain't is more common in uneducated speech than in educated.
Examples:
I ain't going anywhere.
She ain't say that.
I ain't thinking about him.
This suggests that the "correct" usage of ain't is saying am not, are not, or is not. People use this word in their everyday conversation. Should it be accepted as a spoken word of the "Standard English" language? Does using this word classify you as being uneducated....?