tag only collision

Physics
1

how would I make it so that if an object collides with an object that has a certain tag it will do something.

2

You can pick up when an object collides using the OnCollisionEnter function, which can then check the tag on the gameobject of whatever you hit.

For instance :

function OnCollisionEnter(collision : Collision) {
   if (collision.gameObject.tag == "enemy") {
      Debug.Log("Bumped into an enemy!");
   }
}

hope that helps