I would start by clicking on tab Tournaments, tab Scheduled, tab All. Then click on tab Entry twice to sort tourneys by amount. When you see an $11 tourney that is registering, click on register. The ones that accept $11 coupons will bring up a box titled Tournament Registration that has 3 options when you click the drop-down arrow. Option 1 is $10 + $1 Fee, Option 2 is 1100 pts, Option 3 is $11 Satellite, which is your $11 coupon. You would click on Option 3 to register for your tourney.
I sometimes register for a tourney, then I unregister for a tourney just to get some practice getting familiar with the carbon software. I would not do this for a tourney that is doing late registration, though. There is no unregistering for a tourney already started.