The Real-Time Ladder automatically creates games with players currently logged into the ladder. That's why you should leave the ladder when you leave Warzone and are not able to play, as otherwise the ladder may create a game, which you will be booted from. The good news is that if you get booted in the real-time ladder game, you will be automatically logged out of the ladder.
You will be proposed one game at a time. You cannot choose the person to play with - it is random. Also, the map is random. You log in to the ladder, play games, and then log out. It isn't possible to play with the same player more than once every 20 hours.
A player may not play on the Real Time ladder with an account if they have another account which is currently ranked. Accounts become unranked after 3 days of inactivity on the ladder. Violations will be punished with a warning and then a suspension.