Hi!
Check out the documentation: https://marketplace.mendix.com/link/component/2295
What you do is this widget is be able to set an association. So by retrieving the objects over the association you will get the selected objects.
For example if your selectable association runs from Customer to Adress(Customer_Adress). If you want the selected objects Adress, you can just retrieve the Adress objects over the association Customer_Adress in a microflow.
Hope this helps