Hey guero & AnD4D,
Curious which SDK version are you running for MoPub?
This detailed instruction helps with getting setup and integrated: github.com/mopub/mopub-android-sdk/wiki/Getting-Started
Along with creating orders/line items: help.mopub.com/customer/portal/articles/784995-creating-orders-line-items
Please review the guide on how to integrate with Third Party Ad-Networks:
github.com/mopub/mopub-android-sdk/wiki/Integrating-Third-Party-Ad-Networks