This blog defines how to use Popup Control in WPF.

<Window x:Class="LayoutDemo.wndPopup"

xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

Title="wndPopup" Height="300" Width="300">

<Grid>

<ToggleButton IsChecked="{Binding ElementName=pup, Path=IsOpen}" Content="Open Popup" Margin="100" />

<Popup Placement="Bottom" AllowsTransparency="True" PopupAnimation="Fade" x:Name="pup" VerticalOffset="-100">

<StackPanel>

<TextBlock Name="McTextBlock" Background="Black" Foreground="White" >

This is popup text

</TextBlock>

<Button Content="Close this Pupup" Click="Button_Click"/>

</StackPanel>

</Popup>

</Grid>

</Window>