Your story truly begins once you get off the Nautiloid.
Take control of the nautiloid and escape the Hells.
Baldur's Gate Story
Baldur's Gate 3
Playing around with what is possible to say about Baldur's Gate 3. So far spoiler-free, maybe I'll keep it that way. And this would be a good moment to introduce the Community Goals to hide the actual story-related achievements and only have a more generic hint for what to do next.
Achievements
Run around the initial locations: beach, chapel, grove and meet new companions. Eventually you will start discovering mounds of dirt and once you have a shovel start digging.
Dig up five buried chests in a single playthrough - treasure!
You'll probably have a scroll for that already and someone to try and read their mind.
Successfully use Detect Thoughts to pry into someone's thoughts.
Useful but as the loading screen reminds as well - you will lose all the precious loot. So try and shove off someone poor.
Kill a creature with falling damage.
Just play the game and you'll get this one soon.
Complete ten background goals in a single playthrough - you are one with your character.
Same as above: at some point you'll take four long rests, but don't rush it. Four long rests also means there would be four full days of adventures.
Take four full Long Rests in a single playthrough - adventuring's tiring work.
You'll be gathering ingredients all the time. Just visit the potions brewing menu (shortcut is H) and make what looks useful.
Create three unique alchemical solutions in a single playthrough - bottoms up!
At some point you'll meet Lae'zel, and she hits twice. On top, she has the Action Surge ability that grants another attack, and because she attacks twice you now have 4. Eventually, use Pommel Strike bonus action and you've done five attacks in one turn.
Perform five attacks in one turn. Your enemies won't know what hit them (literally).
There will be plenty of literature - books, scrolls, letters and so on. At some point (quite early) you'll naturally reach 100.
Read 100 different books in a single playthrough. Adventuring isn't just daring quests, you know.