I know the contraction of am not, is not, are not, has not, have not, do not, does not, and did not can be represented as ain't. How can I understand correctly which contraction the speaker meant?
Context. "am", "is" and "are" are all parts of the verb "to be", so the subject of the verb will tell you what is meant.
I ain't ready - I am not ready You ain't ready - You are not ready
I ain't got a clue - I haven't got a clue. The got hints we are talking about having or possession.
I think using ain't as a negation of "to do" is much rarer, and if you are in doubt, it's unlikely to be the right answer.