This page describes how to setup your computer and phone for building apps with App Inventor. You can view the video or use the text instructions below.
Open a browser to beta.appinventor.mit.edu Login with your Google account.
App Inventor is mostly a cloud tool but it does require you to download some software to your computer.
Once you've successfully opened the blocks editor, click on New Emulator. Click OK on the dialog that appears. In about a minute, an emulator (an on-screen phone) will appear.
Most people start with Hello Purr, an app in which touching the phone (or clicking the emulator) causes a cat to meow. Get started using this video tutorial