Question

When and how can I use it? When will I use? How it transforms the sentence?

Answer 1

"Ain't" is not proper English!

"Ain't" ISN'T a word! (Not: "Ain't" ain't a word!)

It's typically used by less educated English speakers.

Answer 2

You can use it when you need these: Am not, is not, are not, has not, or have not.

For instance: May ı have some sugar ?I ain't got none,sory.    OR

Are you eating icecream at the moment ?No,I aint. Like that...

Got it ?