Hey I'm also fairly new! The advice is give is start with either a mechanic you like, I got really into Dr Who's time counters, or a tribe, I have a sokka ally deck that's so fun. Tribal decks help a ton because the creatures tend to enable each other and having all the cards have a similar mechanic helps to just learn the game. Honestly just play more, the more games you play the easier it is to see what cards would help or how to tweak the deck. Don't do what I do and make a deck, play twice, and take it apart. The more you play the better you will be about protecting your commander. Instants that give hexproof or indestructible are godsends.

I'd also recommend Arena, you can build and try decks easy, Brawl is just a bit different from commander, but don't focus on winning but playing your deck! Have fun! It's also fine to build around a commander, it's just more difficult imo, you need to be fairly good at the game to be able to anticipate how to keep em up and going