//referencing a gameobject
public GameObject exampleObject;
//===============================================================>
private Rigidbody rb; //example of a component
public void Awake() {
// adding a Rigidbody component to exampleObject
rb = exampleObject.AddComponent<Rigidbody>();
// referencing an existing Rigidbody component in exampleObject
rb = exampleObject.GetComponent<Rigidbody>();
}