Another is for the moments you don't post anywhere else.
Not your 5 best friends, not your 500 followers. The 50 you'd actually invite to your birthday. The ones you want to keep up with without the noise of every other app.
Share what's happening, pick who sees it, scroll through a feed that's only people you know. No algorithm, no strangers. Feel better when you close the app.
Adding someone new: meet in person or find them through mutual friends. That's how it works here.