In following example we are using 4 Label controls. You would see that output is aligned vertically.
<StackPanel>
<Label Content="Stack Panel Demo"
FontSize="15" FontWeight="Bold"
Foreground="Blue"/>
<Label Content="Label1" FontSize="15" FontWeight="Bold" />
<Label Content="Label2" FontSize="15" FontWeight="Bold" />
<Label Content="Label3" FontSize="15" FontWeight="Bold" />
</StackPanel>