How to add, update, remove don't use database

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C#

I'm beginner study C#.I can create form Add,update,delete search use database like SQL Server but I don't know make it if don't use database.You can check my code namespace MODEL or give me a simple project that has the function of add remove update don't use Database to debug.Tks!!!
Sr...My English not good :(

What I have tried:

namespace OBJECT
{
    public class Product_Object
    {
        public string prodid { get; set; }
        public string prodname { get; set; }
        public string cateid { get; set; }
        public string units { get; set; }
        public decimal price { get; set; }
        public bool isAvailable { get; set; }
    }
}
namespace MODEL
{
    public class Product_Model
    {
        private List<Product_Object> LisPro = null;
        public List<Product_Object> Get_Element()
        {
            if (LisPro == null)
            {
                LisPro = new List<Product_Object>();
            }
            LisPro.Add(new Product_Object {
            prodid = "CF1",
            prodname = "Cà Phê Đen",
            cateid = "Drinks",
            units = "Tách",
            price = 20000,
            isAvailable = true
            });
            LisPro.Add(new Product_Object{
                prodid = "F1",
                prodname = "Cơm rang dưa bò",
                cateid = "Foods",
                units = "Bát",
                price = 30000,
                isAvailable = true
            });
            LisPro.Add(new Product_Object{
                prodid = "F2",
                prodname = "Bánh mỳ xúc xích",
                cateid = "Foods",
                units = "Chiếc",
                price = 15000,
                isAvailable = true
            });
            return LisPro;
        }
        public List<Product_Object> Insert_Element(Product_Object obj)
        {
            List<Product_Object> lispro1 = new List<Product_Object>();
            lispro1 = Get_Element();
            lispro1.Add(obj)
            return lispro1;
        }