How to add a moving camera that does not rotate for a third person platformer

How do I add a moving camera that does not rotate for a third person platformer ?
I Wanna make a game like Super Mario 3D World, but the camera keeps rotating, how do I fix that

As I wrote in the comment, I assume that You want TPP camera which just follow a position of the player, but is not turning, as he turns. Something like in Trine, most TPP H&S and such.

using UnityEngine;
using System.Collections;

public class TPP_Platformer_Camera : MonoBehaviour {
    public GameObject target;
    public Vector3 offset = new Vector3(-3,2,3);
    public float damping = 1.0f;
	// Use this for initialization
	void Start () {
	
	}
	
	// Update is called once per frame
	void Update () {
        Vector3 desiredPosition = target.transform.position + offset;
        Vector3 position = Vector3.Lerp(transform.position, desiredPosition, Time.deltaTime * damping);
        transform.position = position;
    }
}

Create camera.
Don’t make it a child of something!
Create a script.
Add it to the camera (drag and drop).
Set Your player as target of camera (drag and drop on the field).
Set offset (You have to tweak it in playmode, and then apply them in editmode).
Set damping (the higher, the faster).
Feel free to tweak values.

If it’s not what You want, please provide picture, sample of game where is it, or better description.

Cheers!