In this article we will be seeing how to create a Custom Silverlight UserControl and Binding the Property. We will use a dependency Property in this example.

Created a Project as SamplePro.
Added an a new User Control as MyNewControl.

Dependency Property:
Now let's add a dependency property. To know more about DP, check out this site:
http://msdn.microsoft.com/en-us/library/cc221408(v=vs.95).aspx

My dependency property code looks as follows:
//  Dependency Property - Begin
        public const string DisplayTextPropertyName = "DisplayText";
        public string DisplayText
        {
            get
            {
                return (string)GetValue(DisplayTextProperty);
            }
            set
            {
                SetValue(DisplayTextProperty, value);
            }
        }
        public static readonly DependencyProperty DisplayTextProperty = DependencyProperty.Register(
DisplayTextPropertyName,typeof(string), typeof(MyNewControl),new PropertyMetadata(String.Empty));
//  Dependency Property - End

The UserControl MyNewControl looks as below:
public partial class MyNewControl : UserControl
    {
//  Dependency Property - Begin
        public const string DisplayTextPropertyName = "DisplayText";
        public string DisplayText
        {
            get
            {
                return (string)GetValue(DisplayTextProperty);
            }
            set
            {
                SetValue(DisplayTextProperty, value);
            }
        }
        public static readonly DependencyProperty DisplayTextProperty = DependencyProperty.Register(
DisplayTextPropertyName,typeof(string), typeof(MyNewControl),new PropertyMetadata(String.Empty));
//  Dependency Property - End
        public MyNewControl()
        {
            InitializeComponent();
            btn.SetBinding(Button.ContentProperty, new Binding() { Source = this, Path = new PropertyPath("DisplayText"), Mode = BindingMode.TwoWay });
        }
    }

MyNewControl is ready for use as shown below:
<UserControl x:Class="SamplePro.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         xmlns:local="clr-namespace:SamplePro"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">
    <Grid x:Name="LayoutRoot" Background="White">
        <local:MyNewControl Width="300" Height="300"  Foreground="Black" x:Name="newcontrol" DisplayText="Hit Me Now !!!"> </local:MyNewControl>
    </Grid>
</UserControl>

Let's give it a run: