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.

Relax.
The Big Bang Theory Season 12, Episode 19

- I don't freaking believe this!
- Relax. It'll be fine.
The Big Bang Theory Season 8, Episode 22

So sit back, RELAX,
and enjoy the following 90-minute video.
The Big Bang Theory Season 6, Episode 20

Hey, why don't we all
just RELAX, huh?
Breaking Bad Season 2, Episode 1

You just... You RELAX all your muscles.
The Big Bang Theory Season 8, Episode 18