Much of it comes to you organically as you play. The game creates events and missions that lead you to its content. Mysterious messages, SOS signals, etc.

It is quite well done. The underlying idea of the game is to explore the universe and be surprised many times along the way. The massive content of the game is well woven into this premise. Basically, just start exploring, follow all the leads and be surprised.

I don't know of guide, but off the top of my head...

Many of these quests result in rewards like ships, appearance modifications, companions, etc.

The timed expeditions typically highlight the new additions. You start them from the Anomaly now; if you don't have access to the Anomaly, follow the mission with "Anomaly" in the name.