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.

• In App Inventor, Click on the Learn link, then the Setup link, and setup your computer.
• Most computers have Java on them already, so for now ignore that step.
• Instead, go straight to Install the App Inventor Setup Software instructions and follow the link for the type of computer you have.
• If you have a MAC: Download the .dmg file and double click it. It may start the install process automatically. If not, look on your desktop and you'll see a mounted disk. Click it, then double click on the .pkg file within it. This will start the install process. After installation completes, you are ready to go.

• Back in App Inventor (beta.appinventor.mit.edu in your browser) choose the New button on the far left to create a new project. Enter a name for the project. This will open the Component Designer. This is where you'll show how the app will look.
• In the Component Designer, click on Open Blocks Editor. A dialog should appear asking if you want to open or save a file named appinventorForAndroidCodeblocks.jnlp. If one option is to open it with Java Web Start, perfect, do so. The process will take up to a minute, so don't get impatient. If after a minute nothing has happened, look in your downloads folder to see if the file is there, and double click it.
• If the system doesn't ask you to open with Java Web Start, you probably need to configure your system with Java (go back to the Learn | Setup screen).
• The blocks editor is where you'll program the behavior of your app, e.g. what happens when the user clicks on a button.

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