Check out example codes for "unity check when clicked on object". It will help you in understanding the concepts better.

Code Example 1

void Update()
{
  // Check for mouse input
  if (Input.GetMouseButton(0))
  {
  	Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
   	RaycastHit hit;
   	// Casts the ray and get the first game object hit
   	Physics.Raycast(ray, out hit);
   	Debug.Log("This hit at " + hit.point );
  }
}

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