A match is rated when it's multiplayer and every player at the table is signed in. Solo matches against the bot and matches against guests don't count.
Everyone starts at 1200. Beating a stronger player gains you more than beating a weaker one, and a draw moves both ratings towards each other.
In games for three or more players, the winner gains against everyone at the table.
You're ranked once you've played 5 rated matches in a game and your profile is public.