In this case, you have five electron domains around the central atom(1 pair and 4 bonds). This means that the general shape is going to be a trigonal planar with a line going through the middle. This would normally form a trigonal bipyrimid. But, one of these domains is a lone pair, so remove a bond from the trigonal plane. This gives you a "V" shape with a line going through the vertex, making a see-saw shape.
