I've just started to learn WPF this week so please accept my apologies if I am being stupid or missing fundamental points!

Iam trying to build a very simple Contact browser. I have a Collection of Contact objects that displayed in a ListBox control which shows the FullName of the Contact and to the right I have a customControl called BasicContactCard. This is the XAML for the ContacWindow that displays the ListBox:

<DockPanel Width="auto" Height="auto" Margin="8 8 8 8">
    <Border Height="56" HorizontalAlignment="Stretch" VerticalAlignment="Top" BorderThickness="1" CornerRadius="8" DockPanel.Dock="Top" Background="Beige">
        <TextBox Height="32" Margin="23,5,135,5" Text="Search for contact here" FontStyle="Italic" Foreground="#FFAD9595" FontSize="14" BorderBrush="LightGray"/>
    </Border>
    <ListBox x:Name="contactList" DockPanel.Dock="Left" Width="192" Height="auto" Margin="5 4 0 8" />
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="1*" />
            <RowDefinition Height="0.125*" />
        </Grid.RowDefinitions>
        <local:BasicContactCard Margin="8 8 8 8" />
        <Button Grid.Row="1" x:Name="exit" Content="Exit" HorizontalAlignment="Right" Width="50" Height="25" Click="exit_Click" />
    </Grid>
</DockPanel>

and this is the XAML for the CustomControl:

 <DockPanel Width="auto  " Height="auto" Margin="8,8,8,8">
    <Grid Width="auto" Height="auto" DockPanel.Dock="Top">
        <Grid.RowDefinitions>
            <RowDefinition Height="1*" />
            <RowDefinition Height="1*" />
            <RowDefinition Height="1*" />
            <RowDefinition Height="1*" />
        </Grid.RowDefinitions>
        <TextBlock x:Name="companyField" Grid.Row="0" Width="auto" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Margin="8,8,8,8" Text="Company"/>
        <TextBlock x:Name="contactField" Grid.Row="1" Width="auto" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Margin="8,8,8,8" Text="Contact"/>
        <TextBlock x:Name="phoneField" Grid.Row="2" Width="auto" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Margin="8,8,8,8" Text="Phone"/>
        <TextBlock x:Name="emailField" Grid.Row="3" Width="auto" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Margin="8,8,8,8" Text="email"/>
    </Grid>
</DockPanel>

The problem I have is how do I bind the individual elements of the CustomControl to the object behind the SelectedItem in the ListBox?