Tilting the game object on the slopes

http://answers.unity3d.com/questions/50774/checking-slope-angle-the-object-is-standing-on.html

What's a collision normal in that?

You can think of normal as a ray that is perpendicular to a surface. If you are using a collision such as what you get from OnCollisionEnter(), then you will get back an array of contact points. You could access the normal for the first contact point with:

 Vector3 v3Normal = collision.contacts[0].normal;

if you are using a raycast to get your hit point, you would get the normal like:

 Vector3 v3Normal = hit.normal;

So I have to shoot ray under my character and get the normal and compare it with angles between them? But how do I get the slope's normal?

 public class AlignWithNormal : $$anonymous$$onoBehaviour {
     
     Ray ray = new Ray(Vector3.zero, Vector3.down);
     RaycastHit hit;
 
     void Update () {
         ray.origin = transform.position;
         
         if (Physics.Raycast (ray, out hit)) {
             transform.rotation = Quaternion.FromToRotation (Vector3.up, hit.normal);
         }
     }
 }