The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

Well, it-it doesn't MATTER!
The Big Bang Theory Season 7, Episode 3

No, it doesn't MATTER. We'll be at work.
The Big Bang Theory Season 4, Episode 6

It doesn't MATTER, I'm not keeping this.
The Big Bang Theory Season 10, Episode 17

But no MATTER what happens
between us, we will always love you.
The Big Bang Theory Season 3, Episode 7

And we will hunt him down
no MATTER where he runs.
Game of Thrones Season 2, Episode 8