I am beginner and i cant get my highscores working

can someone please help me i really dont understand what is wrong.
this is the script:

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";
}
}

 

Start not start. Unity MonoBehaviour messages are case-sensitive.