I am making a 2d shooter with a top view and... my character is a sphere. i want the sphere to collide with a wall (cube). I tried out rigid body but it just makes the wall slide or tumble.
Remove the rigidbody component from the wall, leaving only the collider and the renderers (mesh renderer and mesh filter).
EDIT: If you are using mesh colliders instead of the default sphere-cube colliders, you must enable the property convex in both.
You can either add a Box Collider, or increase the mass of the rigid body so that its much heavier than the sphere.
Add a character controller to your character and move it with the move methods of the character controller. As stated before make sure that you have colliders on your character and the wall.