Use the release button to give the ball an initial velocity up the ramp. Reset will return the ball to the bottom of the ramp.
On its way up the ramp the ramp, the ball will start slowing down due to the force of gravity. This force creates an acceleration in the direction 'down the ramp'. After it reaches the top, and stops moving, the same force will cause it to start sliding back down the ramp.
Link to stand-alone sim: Here is a link to view the sim on its own, with no distractions.