Ain't 和 Don't 的差別在哪裡？如果不好說明，請提供一些例句。

Ain't can be am-not, is-not, or are-not but considered extremely slang and not good for formal writing. "I ain't doing anything wrong". "He ain't going to listen to me". Sometimes ain't can even mean have not, as in "I ain't heard from her in years". All examples that will make an English teacher angry :)
Don't is a simple contraction of do not, you can use it anywhere the longer form fits. "I don't think that's true". "You don't want to eat that". These are less than formal but are acceptable as standard English.