I'll explain it: You can make one alliance with any camper in the game at any time. They will give you two tasks each week. The first task involves pranking someone, which will turn that person into a Frenemy. The second involves hunting monsters, and, during that time, the Frenemy might ambush you and force you to fight different salvos of spiders. After that, if you survive, the Frenemy will call it even, and they will no longer be your Frenemy.

You get a reward for completing two tasks. The first reward is an item from that particular camper, the second is the hockey mask, and the third is either a pair of red cargo pants (for males) or a red skirt (for females)

If you break the alliance, that camper immediately becomes a Frenemy, but you are free to ally with anyone that isn't a Frenemy. If you pick a new alliance partner, you can get different rewards. However, you may only collect one reward a week.

For example, let's say you ally with Duncan. His first reward is his shirt. The second week, you stick with Duncan, and he gives you the hockey mask. On the third week, you break the alliance with Duncan and form one with Geoff. You'll complete his tasks, and get Geoff's hat as a reward.