How can i move a 2D ball ?

I would like to make a game for school on android. So i decided to use a simple ball game. I would like to have a ball in the middle bottom of my device and when i touch the ball, a line or anything else which shows a direction should appear and if i stop touching the ball it should move to this direction.

My main problem is that I am not able to move the ball with the touch.

Can anybody help me ? I am using the lates version of unity now.

Thanks a lot Daniel