Lets assume you have a domain model with Customer entity and Orders entity. Each Customer can have 1 or more Orders.
That should do it.
BTW, you can also do this without a microflow. Simply place an Edit button in the datagrid on the Customer Listing page and select the Order Listing page as your Edit page. Then you can change the Caption and icon of the edit button to indicate that it displays an order listing.
Hope that helps,
To see an example of what you are trying to do, open the Modeler, go to the app store, download the application called My First App. In the MyFirstApp module, open the page called Departments. On that page, is a button entitled Show Members, that calls a microflow to show department member. In this example, the microflow is called from within a Template Grid, but it could also be called from a microflow button place on a datagrid. If you place it on the datagrid, you will need to configure the microflow button to pass the selection to the microflow. This will pass in the row (customer) that you have selected in the datagrid.