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.

We need access
to the MAIN control panel.
Westworld Season 3, Episode 8

No, I stayed off the MAIN streets
and kept checking, so...
Breaking Bad Season 5, Episode 8

I want to see the selfie and MAIN cameras.
Money Heist Season 1, Episode 5

Like Main Street...
The Big Bang Theory Season 2, Episode 5

The ceremony
is traditionally held in the MAIN sanctum,
Game of Thrones Season 3, Episode 4