Check out example codes for "rotatearound unity". It will help you in understanding the concepts better.

Code Example 1

using UnityEngine;//Attach this script to a GameObject to rotate around the target position.
public class Example : MonoBehaviour
{
    private Vector3 target = new Vector3(5.0f, 0.0f, 0.0f);    void Update()
    {
        // Spin the object around the world origin at 20 degrees/second.
        transform.RotateAround(target, Vector3.up, 30 * Time.deltaTime);
    }
}

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