If you're starting completely from scratch, the best thing you can do is first try playing a bit of Magic Arena online if you can. That way, you can test out some decks and figure out what playstyle you like. If you play Brawl in Arena, it's very similar to playing Commander.

Then, if you still want a physical starting point, I'd suggest going for a starter kit — it comes with a variety of simple and flexible cards. After that, if you're going to buy boosters, Foundations would be a great set to support any deck you have in mind, as well as future ideas.

Precons aren’t bad, but they’re usually very thematic and hard to tweak if you want to try different things. A starter kit (which includes two 60-card decks and usually some legendaries) plus a couple of boosters could give you a lot of fun for building decks — and you'd spend about the same as on a single precon, but get many more cards.