It is up to your group how you will pick your rotation site. Your group may choose the point system, the "draw from a card", or something different.
The group point system
You list your choices by 2 grouping - which rotation you really want and where you want to do it (think in excel format with rows and columns). If you don't get your first choice but your second choice instead, you get some points. If you don't get your first or second choice but your third, you get more points. If there is a conflict (let's say there are 2 people who wants to rotate through XYZ hospital for ABC rotation which only has 1 spot), then the person with the most points win (since theoretically that person has been screwed more than the other person). That person (who won) then loses all his/her points while the person who lost that challenge gain more points (since he/she didn't get that rotation). Those points can be used later on when there is another conflict with another student(QRS hospital for EFG rotation)
Sounds complicated but it really isn't once you sit down and think about it.
But it's really up to your group how you guys pick sites. It's possible your group can decide to arm-wrestle if there is a conflict, or pick straws, or use the Harry Potter magic hat. The point-system is just something most groups decide to use since it seems fair and one person doesn't get screwed completely.
Don't worry too much about it until your 2nd year 🙂