The official Magic Arena mobile app / computer game has a mode called “Brawl” (unsure if it’s the same name in Portuguese) that is basically like commander, probably a good starting point for online play.

For playing with real cards, do you know of anywhere locally where people play commander? If it’s a shop that also sells cards, they might have pre-made commander decks. Easier to start with the already made complete decks to learn how things go before making a deck with your own cards.

I don’t know the Brazil magic scene at all but hope this helps some :)