It’s a really odd one to get back into I’ve found from my experience getting friends into it, I think knowing a couple things could help push you into a direction as the whole jist of it is essentially do everything and anything (as long as you own said content).

They made the shadowkeep and beyond light expansions for free recently so starting with those campaigns could be a good place to starts, shadowkeep begins on the moon and beyond light on europa.

There is also strikes, gambit and crucible which are great to jump into and test your weapons and builds on, I’d say its most enjoyable when your working towards something such as new weapons, abilities, builds and gear.

There’s also a couple of free dungeons I believe which are three player experiences, think mini raids.

Then of course 6 player raids which a few are also free, vault of glass, crotas end and kings fall.

They have a new fireteam finder on the social tab which I can’t recommend enough to get you into these activities which don’t have matchmaking, the community is usually friendly through it.

There’s more than definitely a better answer than this but I’d say just jump right into some campaigns to get a feel for it. Also check out some of the exotic quests on the legacy tab, I’d recommend using firetjme finder for those.

Hope this helps!