The “end game content” that’s exclusively things you do at the end of the game is the two raids, “Vault of Glass” and “Crota’s End”. Those things can’t be done without teams and a high enough level character.
The rest of what people mean when they talk about the end game stuff is the progression of how you get up to those higher levels. That’s referring more to things like the “Weekly Heroic Strike” and “Nightfall” missions, which are story missions from the regular game, but with amped up difficulty and rewards.
So once you hit level 20, or the end of your first run through the story missions, whichever comes first, that’s when the game starts to change, because that’s when all the systems about how you acquire and improve better gear start to matter.
Those systems are not well explained though, at least not all of them, and that’s a frustrating part of the game. On one hand, I want to tell you to just play at your own pace and do whatever you’re having fun with, learn it as you go, but I also want to give you a bunch of complicated guidelines and priorities for how best to spend your time and resources to optimize your progression.
I won’t dump a bunch of info on you right now, but here’s one example:
You can find “Ascendant Energy” and “Ascendant Shards” as you play. They’re part of the required materials for upgrading “Legendary” weapons and armor, respectively. There’s going to be a point in the game where you’ll have a few and wonder what the point is. There’s going to be a point in the game where you can’t find enough fast enough. Then there’s going to be a point in the game where they’re piling up in your inventory, largely forgotten.
The public events you stumble upon have a chance to award you with one of these ascendant materials immediately upon completion, and for the first public event you get gold in once a day, you’ll also get a package from the postmaster at the tower that has a high likelihood of awarding you ascendant materials as well (after your first every day, there’s still that chance you’ll get an award for public events, but you won’t get another postmaster reward until the next day). Even less obviously, when you go to the postmaster and claim that reward, you get experience.
So ideally, long before the game has made it clear you’re going to want a lot of ascendant materials, you should be doing at least one public event every day for the reward, because it’s fairly simple and will help down the road. And once you start acquiring weapons and armor that can be leveled up, you also want to be conscious of what you have equipped when you claim that postmaster reward so the experience bonus there goes into the right gear.
Destiny is full of systems like this, and there’s certainly some entertainment and satisfaction in discovering how they work, but I think they left too much of it unclear. I often wonder how much fun I’d be having if I hadn’t been in from day one, and reading reddit on my lunch breaks to keep up as the community figures this stuff out.
So feel free to shout if you’ve got questions any time, I’m always happy to ramble on about it. You’ll have to figure out the balance on your own though, between the potential for frustration with unclear game systems, and the frustration of feeling like you’ve got to do homework just to play the game right.
That’s a really negative note to end this post on, so I should reiterate: this game can be really frustrating, but I really really like playing it.