I need help on my Pokemon Platinum game?

I need help on Amity square! How do you get the pokeball on top of the ledge on the right side of the lake? There is a man standing on another ledge too, how do you talk to him? I've realized when you walk inside a ruin, you teleport to another ruin. But I haven't found a way to get to the ledges. Since there's a pokeball on top of one of the ledges, I'm guessing you're supposed to get to it somehow. Sorry for asking too many questions!