how to instantiate an object as a child in unity code example

Example 1: how to instantiate as child unity

Instantiate(obj, pos, rot, parent);

Example 2: unity create a child object

// spawns object
        objToSpawn = new GameObject("Start");

        // add Components
        objToSpawn.AddComponent<Rigidbody>();
        objToSpawn.AddComponent<MeshFilter>();
        objToSpawn.AddComponent<BoxCollider>();
        objToSpawn.AddComponent<MeshRenderer>();

        // sets the obj's parent to the obj that the script is applied to
        objToSpawn.transform.SetParent(this.transform);