Ain't is not proper English, it is slang from the Southern United States. But Americans from all over the country will sometimes use ain't, and in all cases it means is not/are not. examples: He ain't coming. They aint going to be there. There ain't no sense in arguing on the internet, it's like trying to win a gold medal at the Special Olympics! (just kidding) I ain't racist.

http://www.italki.com/answers/question/172581.htm#.UNFUM283aNI Read those answers please. "ain't" and "isn't" mean the same now. But you shouldn't use "ain't" because it's a slang.