Sadly, I'm a newbie myself!
I'm a bit confused by the whole Horizons / Beyond thing. Horizons seems to be a separate game which you had to buy when it was released, although it seems to be bundled with Elite Dangerous on Steam, because I have it and I didn't buy it separately. Beyond looks like it's just the most recent expansion, and is free for players of either Dangerous or Horizons?
When I start the game from Steam, I can choose to launch either Elite Dangerous or Elite Dangerous: Horizons, but not Elite Dangerous: Beyond. So I guess Beyond is just bundled into both options. I chose Horizons because it seems like it's just additional stuff on top of the basic game, so it does no harm to pick that option.
Sometimes I think they like to make everything about this game as impenetrable as possible, or maybe it's just because we're new to the party