Portals send pieces to different parts of the field. If they go through a Blue Portal, they come out of a Yellow Portal. Remember that some Portals might be located next to each other, while others might be far apart.

Why aren't pieces falling down? Make sure there's enough room under the Yellow Portals, and, if you need to, make some moves to make more room! There might also be an obstacle at the entrance to a Blue Portal or at the exit from a yellow one. Remove them to clear the way for pieces.