Character is floating

using UnityEngine;
using System.Collections;

public class AutoMove : MonoBehaviour {

    public float speed;

    private void Update() {
        
    
    

                transform.position = new Vector3((transform.position.x + speed), 0, 0);


        
    }
}

When I go to play mode my character is floating:

settings:

I have no idea why it happens, please help me.

Add a rigidbody2d component