See the below code:-

 class Order
 {
 public int Id;
 public string Name;
 }
 class OrderItem
 {
 public int Id;
 public string Name;
 public int OrderId;
 }
 public class Program
 {
 static void Main(string[] args)
 {
 var orders = new List<Order> {
 new Order { Id = 1, Name = "One" } ,
 new Order { Id = 2, Name = "Two" }
 };
 List<OrderItem> orderItems = new List<OrderItem>
 {
 new OrderItem { Id = 1, Name = "Item One", OrderId = 1 },
 new OrderItem { Id = 2, Name = "Item Two", OrderId = 1 },
 new OrderItem { Id = 3, Name = "Item Three", OrderId = 1 },
 new OrderItem { Id = 4, Name = "Item Four", OrderId = 2 },
 new OrderItem { Id = 5, Name = "Item Five", OrderId = 2 }
 };
 var results = from order in orders
                            join orderItem in orderItems on order.Id equals orderItem.OrderId into GroupOrderItems
 select new { order, GroupOrderItems };
 //Just to write the results to the console
 string columns = "{0,-20} {1, -20}"; 
 Console.WriteLine(string.Format(columns, "Order", "Item Count"));
 foreach (var result in results)
 {
 Console.WriteLine(columns, result.order.Name, result.GroupOrderItems.Count());
 }
 Console.ReadLine();
 }
 }

public static void LinqJoin()
{
IList orderItems = new List() {
new OrderItems(){orderId=1, orderName=”Soap”},
new OrderItems(){orderId=2, orderName=”Shampoo”},
new OrderItems(){orderId=3, orderName=”Moisturiser”}
};
IList orderCount = new List(){
new OrderCount(){orderId=1, count=3},
new OrderCount(){orderId=2, count=4},
new OrderCount(){orderId=3, count=8}
};
var joinResult= from items in orderItems
join oc in orderCount
on items.orderId equals oc.orderId
select new {
orderItem=items.orderName,
count= oc.count
} ;
foreach(var item in joinResult)
{
Console.WriteLine(item.orderItem + “ :”+ item.count);
}
}

public class OrderCount
{
 public int orderId { get; set; }
 public int count { get; set; }
}
public class OrderItems
{
 public int orderId{ get; set; }
 public string orderName{ get; set; }
}