Kikuchiyo

You get 10 guaranteed days off, plus 2 "Optional" days off. Optional means the company can buy them back or shift those 2 days at will. But the 10 "Guaranteed" days off are yours. Those are often, but not always, in a single 10-day block.

Bid packages have some lines of known flying and many lines with some or all reserve (called "standby" here.) However, the flying is so fluid as new business gets added as the month goes on, that all schedules are subject to change. Best advise is to simply bid for the guaranteed days off you want, and then fly where they send you.