Your group will be picked up from the hotel and taken to one of the top Riga's night clubs. The group will have listed entrance, so they will jump the main queue. However there could be smaller VIP queue.
The guide will lead your group into the club and then leave. You are free to stay there as long as you wish to. Once you will be ready to leave you just need to call and your group will be collected and transferred back to the hotel. Clubs in Riga get busy after midnight and stay open till about six in the morning.