About OOP, using PHP

Question

I have a database connection class, in which i am using a constructor for connection. I have another class(class Product). How do I get the $conn variable from the class database connection into the class products so that I can use the variable for executing my queries ? . Here in my code I want get the database connection variable from class DatabaseCon ($this->conn) into the class Products method getProducts() so that i can use it in mysqli_query(connection variable here,$sql). Currently I am inheriting the class DatabaseCon into class Products and it is working but i want to know if this is the correct way of doing it or not.

<?php
    class DatabaseCon
    {
        function __construct()
        {
            **$this->conn** = mysqli_connect("localhost","root","qwerty","mss");
            if($this->conn)
            {
               // echo "Connected";
            }
            else
            {
                echo "Error : Not connected";
            }
        } 
    }
 ?>  



<?php
require 'db_config.php';
class Products extends DatabaseCon
    {
      function getProducts()
         {         
          $sql= "SELECT * FROM products";
          $row= mysqli_query(**$this->conn**,$sql);
          $result= mysqli_fetch_all($row,MYSQLI_ASSOC);
          return $result;
         }
    }
?>