Follow along with this INTRO TO APP INVENTOR 2: Part 2 - Design Interface. App Inventor is the MIT developed web-based integrated development environment (IDE) originally developed by Google.

MIT App Inventor is a web-based integrated development environment (IDE) originally developed by Google, and now maintained by the Massachusetts Institute of Technology (MIT)’s Computer Science and Artificial Intelligence Lab. It uses a graphical user interface (GUI) very similar to the programming languages Scratch (programming language). Users can drag and drop visual objects to create an application that can run on mobile devices.