1. When a marble is stil, what forces are acting on it?

Question

2. Which force is responsible for a motion of a ball?

Answer 1

gravity and centripital force.  If your foot impacts it, the inertia of your foot is transferred into the ball and the inertia of the ball is transferred to your foot.  The net result usually sends the ball careening for a SCORE.

Answer 2

I would say gravity and inertia are acting on the still marble.  Gravity will affect the trajectory of a thrown or dropped ball.