Fly up to any spaceship in the galaxy and dock with its airlock to sneak inside. From there, you've got to sneak up on the crew and either outshoot or outthink them. Take missions to steal loot, assassinate VIPs, or rescue friends.
There may be additional achievements or trophies depending on your console, region, or version of the game. Creating a video guide for any of the achievements with bounties will award you with gold.