how to do collision detection in unity code example

Example 1: unity how to make two objects not collide

void OnCollisionEnter(Collision collision)
  {
      if (collision.gameObject.tag == "theobjectToIgnore")
      {
          Physics.IgnoreCollision(theobjectToIgnore.collider, collider);
      }

Example 2: check for collision unity c#

void OnCollisionEnter(Collision col) { }

Example 3: how to do collision tag in unity

void OnColliSionEnter2D(Collision col){
   if (col.gameobject.tag == "Enemy"){
        Destroy(gameObject)
        }
}

Example 4: how to get collision in unity

//this is the function to test for collision
void OnCollisionEnter(Collision collision)
{

//Use this function to provide a collision interface with any object using the name of the object
if(Collision.gameObject.name == "Name of object")
{
/*Code 
here
*/
}
//Use this function to provide a collision interface with any object using the object's tah
if(Collision.gameObject.tag == "Tag of object")
{
/*
Code 
here
*/


}
}