Short answer: it puts a tiny animated character of your partner on your browser, and they see yours on theirs. You pair with an invite code, and a wave, hug, kiss or mood plays on the other screen.
What it shares: only your online status and what you send. It never reads which sites you visit, your tabs, or what's on the page. The site permission is optional and only lets the character appear on pages.
Do not disturb hides it and silences everything until a time you choose, and your partner sees "busy until 3:00 PM".
