how to reference serializable class unity code example

Example 1: unity serializable

using System;
using UnityEngine;public class Player : MonoBehaviour
{
    //Create a custom struct and apply [Serializable] attribute to it
    [Serializable]
    public struct PlayerStats
    {
        public int movementSpeed;
        public int hitPoints;
        public bool hasHealthPotion;
    }    //Make the private field of our PlayerStats struct visible in the Inspector
    //by applying [SerializeField] attribute to it
    [SerializeField]
    private PlayerStats stats;
}

Example 2: how to access serializable class objects unity

public class A1 : MonoBehaviour
{
    User1 user = new User1();

    private void Start()
    {
        user.Start();
    }

    public void OnMouseDown()
    {
        Debug.Log(user.BB);
    }
}