Please help i dont seem to get HighScore saving to work

Unity Engine
1

I am a beginner and i have no idea why it is not saving :/.
Maybe some experts can help me. what is wrong with the code.
Also please give me instructions where i need to add this script, what to connect to eachother ect!

using UnityEngine;
using UnityEngine.UI;

public class Score : MonoBehaviour
{
    [Header("Please Drag Objects Here")]
    public Transform player;
    public Text currentScoreText;
    public Text highScoreText;

    private const string highScoreKey = "HighScore";

    [Header("Do not change values")]
    [SerializeField] private int highScore = 0;
    [SerializeField] private int currentScore = 0;

    private void start()
    {
        highScore = PlayerPrefs.GetInt(highScoreKey, 0);

        highScoreText.text = highScore.ToString();
    }

    private void Update()
    {
        currentScore = Mathf.RoundToInt(player.position.z);
        currentScoreText.text = currentScore.ToString();

        if (currentScore > highScore)
        {
            highScore = currentScore;
            highScoreText.text = highScore.ToString();

            PlayerPrefs.SetInt(highScoreKey, highScore);
            PlayerPrefs.Save();
        }
    }

    private void OnDisable()
    {

        PlayerPrefs.SetInt(highScoreKey, highScore);
        PlayerPrefs.Save();

        Debug.Log("I'm being Disabled! The high score is currently: " + highScore);
    }

    public void Reset()
    {
        PlayerPrefs.DeleteAll();
        highScoreText.text = "unset";
    }
}
2

Since you are starting out, your questions are too basics, to explain in few words.
Not knowing what you know, or don’t, I suggest you start with
Getting Started