How do I make a spring on a cube?

Guys I am new in unity and I want to know how to make the ball bounce everytime it hits the cube I made. thanks. Btw , the ball is the gameobject and I really need help. thanks10547-2013-04-30_115203.png

add a rigidbody, that will enable physics.

If you fiddle with mass you can make the object lighter so it bounces on impact better.