How to pass data between two user controls in WPF?

Question

Hi,

I have two user controls and a windows form in my WPF application. When I click on a combo box item in one user control(SideMenu), the window form loads and display few values. I have to select a value from this windows form and display it in another user control(StudentDetails). 

Both the user controls are present in the MainWindow.Xaml.

<local:SideMenu Margin="0,16,10,-290" Grid.ColumnSpan="1" />

 <local:StudentDetails Margin="10,0,-280,-234" Grid.Column="2" Height="Auto" Width="Auto" />

Since I am new to WPF , I do not know how I can achieve that. Please help me.