The administration module is not needed in case you are developing a mendix app for mindsphere – as the leading user management system is MindSphere. Users are created automatically and assigned the corresponding user roles inside your Mendix app during during SSO when user opens the app from MindSphere launchpad.
To get started please use the “Siemens Mindsphere Starter Application” from here: https://marketplace.mendix.com/link/component/109130
Everything you need is integrated here.
Details about the single sign on process can be found here:
Also a good starting point is the tutorial “Build a MindSphere app with Mendix” in the academy: https://academy.mendix.com/link/path/80/Build-a-MindSphere-app-with-Mendix