The IEnumerable<T> is used to iterate a read only collection. It has only one method GetEnumeartor() which allows you to iterate the read only collection using a foreach loop. It only iterates in the forward direction.  IEnumerable <T> is defined in as follows:

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading;
namespace Forum
{ 
public class ChildClass 
{
      static void Main(string[] args)
        {
            List<Customer> CustomerList = new List<Customer>();
            Customer obj = new Customer();
            obj.CustomerID = 1;
            obj.CustomerName = "Visal";
            obj.ContactNumber = "8787878787";
            CustomerList.Add(obj);
            obj = new Customer();
            obj.CustomerID = 1;
            obj.CustomerName = "Visal";
            obj.ContactNumber = "9797979797";
            CustomerList.Add(obj);
            obj = new Customer();
            obj.CustomerID = 1;
            obj.CustomerName = "Visal";
            obj.ContactNumber = "77986521322";
            CustomerList.Add(obj);

            IEnumerable<Customer> EnumList = CustomerList;

            foreach(Customer o in EnumList)
            {
                Console.WriteLine("CustomerID: {0}",o.CustomerID);
                Console.WriteLine("CustomerName: {0}", o.CustomerName);
                Console.WriteLine("ContactNumber: {0}", o.ContactNumber +"\n");

 }
          Console.ReadLine();
        }
    }

public class Customer
{
        public int CustomerID { get; set; }
        public String CustomerName { get; set; }
        public string  ContactNumber { get; set; }
    }
}