Why Bring one? You don't 100% have to bring one. they are kind of a luxury item on warm nights where you are not expecting rain. Then you can just use a tarp to put under you.

What kind should I get? A tent helps keep you warmer than a tarp would. However, they are much heavier and can be slightly easier to set up. My dad and I just bring three tarps. We normally sleep separate, each one of us claiming our on plot of land. But, if the night gets wet (foggy), we put up the third tarp and then sleep under it. It is a pretty easy plan. However, the tarps really only protect you from water.