Bind to an Existing Object Instance

   
  
<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="WPF" Height="140" Width="300">
    <Grid Margin="4">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="80"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>

        <Grid.RowDefinitions>
            <RowDefinition Height="30"/>
            <RowDefinition Height="30"/>
            <RowDefinition Height="30"/>
        </Grid.RowDefinitions>

        <TextBlock Margin="4" Text="First Name" VerticalAlignment="Center"/>
        <TextBox Margin="4" Text="{Binding Path=FirstName}"
                 Grid.Column="1"/>
        
        <TextBlock Margin="4" Text="Last Name" Grid.Row="1" VerticalAlignment="Center"/>
        <TextBox Margin="4" Text="{Binding Path=LastName}"
                 Grid.Column="1"
                 Grid.Row="1"/>
        
        <TextBlock Margin="4" Text="Age" Grid.Row="2" VerticalAlignment="Center"/>
        <TextBox Margin="4" Text="{Binding Path=Age}"
                 Grid.Column="1"
                 Grid.Row="2"/>
    </Grid>
</Window>
//File:Window.xaml.cs
using System.Windows;


namespace WpfApplication1
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
            this.DataContext = new Employee()
                                   {
                                       FirstName = "A",
                                       LastName = "B",
                                       Age = 26
                                   };
        }
    }

    public class Employee
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public int Age { get; set; }
    }
}