There's a fun little thing you can do here. Jump over the Koopa shell and step on the P-Switch. The shell will fall down and the shellless Koopa will kick the shell down to the group of red Koopa Troopas. Follow the shell and you'll get lots of points and, if you're lucky, even a 1-Up.
Otherwise, just run forward, go through the pipe and step on the green switch in the next room. This activates all green switch blocks in the game!
