The companion

Appearance: a small flying bot with a heart antenna that hovers next to you. Its face changes between happy, talking and working.
Building: it flies to ghosts within your work radius (25 tiles by default), builds them and takes the items from your inventory. If you're out of the item, it complains.
Deconstruction: it removes things marked for deconstruction and puts the loot in your inventory. If your inventory is full, it complains about that too.
Name: it's called Sprocket by default, but you can rename it in the mod settings.

The chat

Random chatter: every 90–240 seconds it asks how your day is going, checks if you've eaten, roasts your belts, and says wholesome or lonely-person jokes.
Biter reminders: it nags you about biter expansion, shows the real evolution percentage, and mentions pollution levels. If you've turned expansion off, it teases you about that instead.
Context lines: it reacts to night, driving, low health, an empty research queue, your hours played, and standing still too long.
Replying to you: type in chat and it answers. It picks up on hello, thanks, sad, love, questions and so on. Telling it to shut up mutes it for 5 minutes.
Hugs: /hug gives it a hug.
Testing: /clingy makes it talk right away, and /clingy expansion forces a line from a specific pool.
Text bubbles: the same lines also show above its head, and you can turn that off.