App Inventor is an online tool, meaning you can create apps for phones or tablets right in your web browser. This website offers all the support you'll need to design apps:

Setup Instructions for Testing: Set up your iOS or Android phone or tablet for live testing. (Or, start the emulator if you don't have a mobile device)

Designer and Blocks Editor Overview: Tour the App Inventor environment

Beginner Tutorials: Jump in and get started programming in App Inventor

Sharing and Remixing Apps: Share your app code with friends to load in App Inventor and remix

Building and Installing Apps: Build your app for installing on a phone or tablet (Android only, for now)