This applet should help you to see the effects of changing various parameters (a, k, and h) in the function y=a(x-h)^2+k.
Suggested activities: 1) Start by just changing h, then move the point A around. 2) Set h=0 and try changing k. Move A around again. 3) With k not equal to 0, try changing h again and moving A. 4) Can you make a general statement about the effects of changing h and k on the graph?