How to create a player class and make 2 instances of the player, and handle different input key for each player?

Hello, I am very new to unity, I followed the Roll a Ball tutorial here https://unity3d.com/learn/tutorials/projects/roll-a-ball/displaying-text?playlist=17141

I successfully made a one player game. And now I want to make a 2 players game in the same script. How do I create a player class and handle the different keys for 2 players' movement? I attach my code here. I attach the same script to the two players, now it does not move independently because I have not created a class or handle the input in my script.

Thank you for your help!

Code:

 public float speed;
 private Rigidbody rb;
 public Text gameText;
 public Text keyText;

 // Use this for initialization
 void Start()
 {
     // associate the rb object with players, and initiallize UI texts

     rb = GetComponent<Rigidbody>();
     gameText.text = "";
     keyText.text = ("Move keys: ←↑→↓");

 }
 // Update is called once per frame
 void Update()
 {

 }
 void FixedUpdate()
 {   //move the player by input keys

     float moveHorizontal = Input.GetAxis("Horizontal");
     float moveVertical = Input.GetAxis("Vertical");

     Vector3 movement = new Vector3(moveHorizontal, 0.0f, moveVertical);

     rb.AddForce(movement * speed);
  
 }

}