3/2 means each player gets 3 minutes for the whole game plus an additional 2 seconds increment per move. Rapid games are therefore longer than Blitz games which in turn are longer than Bullet games.
The 2 seconds increment per move does not add to your timer. You get a 2 seconds timer per move. Standard title matches are 3 minutes per move averaged, but given as 2 hours for first 40 moves, then 1 hour for the next 20 moves. Title matches end at 60 moves.