e5 is part of the center, like d4, d5, and e4. Some benefits to controlling the center of the chess board with your pawns: (1) It gives your bishops and knights more room to maneuver--and good players can often convert better space and mobility into a material advantage (2) If your opponent tries to develop his pieces, you can often gain time demobilizing them by advancing your pawns.
e5 and positional advantages

Why is having control of e5 important? I know you can access more squares from that square, but is it really all that important? What are some important positional advantages, and how/where can I learn them?