How can you use "ain't" correctly? You don't. It's not proper English. Very few English speakers use it anymore. It is a southern American (US) historical word. If you are trying to be funny and imitate a southern drawl, go for it. Otherwise skip it.

To be honest, if you are not from a place, or social group where "ain't" is used, as part of the dialect, you generally can't use it correctly. One exception would be if you were trying to sound like someone from a place or social group like that. That might not be wise, as you might sound like you were making fun of that accent.

"Ain't" is the colloquial version of "isn't" or properly "is not". For example: "This answer ain't the right one" or "Boy, i ain't your mother".

Ain't = are not./is not. It is a contraction, a short form of "are not". It is slang, but is common and acceptable english. Eg. That ain't bad = that isn't bad. We ain't got no milk (from a film) = we do not have any milk Ain't that so? = isn't that so (isn't that correct)

English speakers use it to avoid having to conjugate the verb to be. "Ain't" is used for all persons (I, you, he, etc.).