These are Mendix basics, which are explained in the Mendix learning paths; https://learn.mendix.com/link/path/10
I believe this would be a help for you to implement the above. You can use CustomString custom widget from Appstore.
1. In Page1 Dataview of the Customer entity place two CustomString(Context) and display the CustomerID and OrderNumber returned by the source MFs of both the added widgets.
2. Configure two MFs for setting them as onClick MFs for both the widgets.
3. One MF will be passing your Customer object to Page 2 which will have a DataView to receive the object and display the Customer details/attributes.
4. The other MF will be retrieving your Order from the Customer association and pass the object to Page 3 which will have a Dataview to receive the object and display the Order details/attributes.
Hope this works for you!