How do I make a ball move when it is collided with?

I am doing my A-Level project and I have started making my game in unity. The game is a football penalty game that should allow the user to select the power and direction of the penalty. However, I am having difficulties making the ball move when it is collided with by the characters foot. I'm very new to Unity and I have only started using it to create my game for my project, so any help would be appreciated!