Answer 1

Hello Jai.
I'm unable to give you a clear, clean answer covering all those concepts but...

I recommend you to complete the C tutorial.

Structures and typedef:
https://www.sololearn.com/learn/C/2942/?ref=app
Unions:
https://www.sololearn.com/learn/C/2944/?ref=app
Consider taking a deep look at the comment section of both lessons aswell.

Also use the search bar 🔍 feature here in Q/A Discuss section before asking a likely-asked-before question as suggested in the community guidelines.

What are enums?↓
https://www.sololearn.com/discuss/1022363/?ref=app
https://www.sololearn.com/discuss/1822606/?ref=app

Structure vs union↓
https://www.sololearn.com/discuss/1865420/?ref=app
https://www.sololearn.com/discuss/96904/?ref=app
https://www.sololearn.com/discuss/1819138/?ref=app
https://www.sololearn.com/discuss/1494234/?ref=app

And there are more...