Amazon cloud based App as Restful Services with backend in Java and frontend in Android

The question is too abstract after days of search I could not find solution.I am going to develop an open source Student Scheduling System which will help student in their studies.The goal is to build a complete mobile app with REST API and a powerful backend (in java) running in the cloud(amazon).I know the basics of all involved technologies in project like jEE,Gradle,Android,Amazon,Sprint MVC and Tomcat. I have learned all these technologies individually.What I do not know, how all these technologies work together? What should be my first Step towards developing?