How to bind combobox in WPF in C#.Net?

Question

 Hello everyone,

 

I have arraylist users. 

 

How can I add combobox Zeroth position defult text?

 

<ComboBox ItemsSource="{Binding UserName}" Name="cmbUserName" Height="30"
          VerticalAlignment="Top" Margin="10,64,614,0"/>

var logList = service.GetLogDetails();
var UserName = (from A in logList orderby A.FirstName select new UserName { Users = A.FirstName + " " + A.SurName, ID = Convert.ToInt32(A.Id) }).Distinct();

cmbUserName.Text = "Username";   /* How can I add combobox Zeroth position text? */
           cmbUserName.ItemsSource = UserName;

 

 
I want to add these usernames in Combobox and set ID. Then, pass ID where combobox on change. How can I do this?