“Activities” in Starfield are effectively small nudges for the player to explore, that will lead to various other more meanwhile activities, usually a fully-fledged mission. A lot of the time these Activities will be based on conversations you overhear, or hints that the game gives you, that will open up into much larger opportunities. Starfield is packed to the rafters with these kinds of things, so if you hear a conversation break out, stick around and let it populate your log, and then see where it goes.

A non-exhaustive example of these Activities that may pop up at one time or another are as follows:

• Check out the Constellation Board.
• Follow Noel when first in The Lodge, after asking her where you can stay.
• Speak to the security guard in the booth near the spaceport in New Atlantis, to discover about "brown-outs" in The Well, a district in New Atlantis.
• One of them will pop up telling you to check out your ship’s inventory when you get back on the Frontier.
• If you watch the encounter by the elevator in Neon, the activity "Talk to Saburo Okadigbo" will appear in your list.
• If you speak to Donna Rain, the janitor, in the MAST District, near the tram, she'll ask you to fetch her a Terrabrew Cappuccino.
• If you ask about Vlad's home in the Eye, he'll ask you to visit his home and make sure it's still standing.
• After overhearing a conversation in New Atlantis, the activity "Talk to the Scientist by the tree" will end up in your Activities tab.
• "Look for the Opportunity Rover on Mars" will be an Activity you can get from reading a sign near a Mars attraction in one of the game’s later missions.

My Activities list is fully populated even now, after having finished 46 of them already. I have numerous “Speak with/Talk to” Activities all ready to follow up on (including talking/speaking to Trevor, Laylah, Zinaida (at the Gagrin Recruitment office), “Doc” Manning, Tevin Anastas, Frank Renick, Borealus, Hamza, and so on). 

My point is, you won’t be short of Activities to do and follow-up on in Starfield. Just stop and listen (and watch) every once in a while to conversations happening in the major cities and settlements, to see where they go.

Check off 30 of these and you’ll unlock this achievement.