In maze, pong, or collide type games, you usually want a sprite to bounce back or move when it touches an edge or an object. This can be accomplished by using a Sensing block such as the ones shown to the left. These blocks are usually placed in a block and then an block (which are Control blocks) along with Motion blocks that tell the sprite how far to move. The sample at the right tells the sprite to turn right 180 degrees and then move 10 steps.
Click on the image on the right to see more.