Entediado na aula de c#

foo.cs

using System;

public class FOO {

 public static void Main() {
  var category = new Category("Maquiagem");
  var product = new Product("Vareta", "vitor@gmail.com", category);

  var categoryRepository = new CategoryRepository();
  var productRepository = new ProductRepository();

  Console.WriteLine(category.mandaLetra());
  Console.WriteLine(product.mandaLetra());

  productRepository.Insert(product);
  productRepository.Update(product);
  productRepository.Delete(product);

  categoryRepository.Insert(category);
  categoryRepository.Update(category);
  categoryRepository.Delete(category);
 }

 
 public class Category: BaseModel {
  public String name;

  public Category(String name): base() {
   this.name = name;
  }

 }

 
 public class Product: BaseModel {
  public String name;
  public String email;
  public Category category;

  public Product(String name, String email, Category category): base() {
   this.name = name;
   this.email = email;
   this.category = category;
  }

 }

 
 public class ProductRepository: BaseService < Product > {
 }

 public class CategoryRepository: BaseService < Category > {
 }

 
 public abstract class BaseModel {
  public int id;

  public BaseModel() {
   this.id = generateId();
  }

  public int generateId() {
   Random randNum = new Random();
   return randNum.Next(100000);
  }

  public String mandaLetra() {
   return "Salve -> " + this.ToString();
  }
 }

 
 public abstract class BaseService < T > {

  public void Insert(T item) {
   Console.WriteLine("Aeeee cadastrou");
   Console.WriteLine("\n\n " + item.ToString());
  }

  public void Update(T item) {
   Console.WriteLine("Aeeee atualizou");
   Console.WriteLine("\n\n " + item.ToString());
  }

  public void Delete(T item) {
   Console.WriteLine("Aeeee deletou");
   Console.WriteLine("\n\n " + item.ToString());
  }
 }

}