This feels like an MMO, idk if im up for it tbh lol
Start with the New Light Campaign. If you NEW new, it should automatically load up, if not go to the kiosk at the tower/helm to pick it up.
4 elemental subclasses to know 3 light (Arc, Solar and Void) and 1 dark (statis) and the elements basically have different effects on enemies.
Pick up bounties from the tower vendors and planetary vendors for extra XP and to get the hang of things, you might want to do public events at the Cosmodrome.
Play through the campaigns (Shadowkeep, Beyond Light & Witch Queen) to get the story and why certain characters matter.
and do Strikes/Gambit/Crucible to get the hang of things and clique up with people you play with