Basically, support are champions who are pretty strong with minimal items, so the idea is for you to build gold generation items like philosopher's stone and heart of gold, try to give map control through wards, and eventually get very cost efficient aura items like Aegis of the Legion, Zeke's Herald, etc.
Supports are paired with AD carries, since they're the champions that scale the best with gold and don't gain as much punch from levels as mages, so being in a duo lane doesn't hurt them that much, and can be protected much better with a support.
It's a common misconception that playing a support is pretty boring. Assuming the players are around the same skill, supports are actually the ones who make plays in lane and usually determine who wins the lane. They're the ones who should be doing most of the harass, zoning, and foiling and setting up ganks.