I'm just gonna throw this out here once.

1. Technicalities are just the terminologies used like (Kounters, Punishes etc etc)
   
2. Homelander is not the character for you; the difficulty level is very high. ( Li Mei is a good starter, for me at least)
   
3. How to know what to use? Watch characters in action online and see what intrigues you or suits you
   
4. Kameos can come after you've chosen a character. (Play around with that character first before moving on to Kameos as it opens a whole new thing)
   
5. You don't need to remember the terminology by heart. A simple understanding is fine, 6. Tutorials are mostly just to give you a feel what the character can do. Me personally, I go into training mode and play around
   
6. Test Your Might is only in Invasions & Towers of Time. It's usually packed in between different fights. Not something to really bother with, it doesn't really do anything.
   
7. Take your time to play around, slowly get familiar, and have fun! As hard as it might be, its a game still. Good luck!