How To Move A Ball Using Touch Input?

Hey everyone, I am pretty new to Unity3D, so that's my excuse if this question is stupid...

I want to move a ball around, however, I want to move it around using touch input. The ball would have a rigidbody body.

I would be using 4 buttons; up, down, left, and right in order to move the ball.

For example, I would like to AddForce to the ball, and move it to the right, when the right button is pressed.

How would I do this? And also, how would I make it so that a picture or texture or whatever becomes in button on the scene? By the way, I work with C#. :)

Thanks!