How do I make a Countdown Timer in Minutes and Seconds only

I have most of the code for the countdown timer . It’s still not working . The timer counts down one number and it stops. I am also trying to display the timer on the screen. Here is some of my code :

using UnityEngine;
using System.Collections;

public class clock : MonoBehaviour {
public string Minutes;
public string Seconds;
public float Clock;
void Start ()
{
string Minutes = Mathf.Floor(Clock / 60).ToString(“00”);
string Seconds = Mathf.Floor(Clock % 60).ToString(“00”);

}


void Update () 
{ 

``Clock += Time.deltaTime;

}

}

You can try with this:

public class Clock : MonoBehaviour
{
    public float CurrentTime;
    public float Minutes { get { return Mathf.Floor(CurrentTime / 60f); } }
    public float Seconds { get { return Mathf.Floor(CurrentTime % 60f); } }

    private void Start()
    {
        CurrentTime = 0f;
    }

    private void Update()
    {
        CurrentTime += Time.deltaTime;
    }
}