Every pilot bids in the first round. There are generally 3 different kids of lines: regular (consisting of normal pairings - 1,2,3, or 4 day), reserve (all 3, or 4 day blocks of reserve), and blank lines. If you get a regular or reserve line, you know your schedule on the 9th of the month for the following month. If you get one of the blank lines, you participate in the 2nd round. The second round is much smaller and the lines are constructed from whatever was dropped due to conflicts after the first round was awarded. Most of the lines consist of regular pairings, but there may be reserve blocks mixed in. If you participate in the 2nd round, you'll know your schedule for the next month on the 19th of the preceding month. It all makes more sense after you bid once or twice. It's a pretty good system with a lot of flexibility.