Move and control a sphere on irregular terrain and keep it on top of that terrain

Hello, I have two problems: The first problem is that I was trying to move around a sphere on my terrain, but it keeps going down the map. I was using the “constant force” component as gravity to get the effect of being pulled down. Also, I was trying to figure out how to control my sphere in order to rotate in the direction that’s moving and here is the second problem: I cannot make the sphere to move, I tried many codes from the community of unity but none of them made it move, so, can someone help me?

I used that once to have a sphere constantly hovering around 3f above irregular terrain tagged as “ground” :

if (Physics.Raycast(transform.position, Vector3.down, out hit, 3f)) 
            if (hit.collider.gameObject.tag == "Ground") transform.position += Vector3.up / 10;