The instructions do seem to be a bit light on it.
But it's pretty easy to figure out after you know to right click on one of the image points for a pop up menu.
Set the shape to match your character/object, so it reacts with the environment correctly.
Remember however that the number of points is checked for collisions every tick, so it will warn you not to use over 8 per sprite.
(edit: made the link clickable)