Installing App Inventor Emulator (only do this if you don't have an Android):

Installing App Inventor 2 Setup on Mac OS X

To get the Android emulator for your Mac, download and install the Setup Package. Click the blue link below to begin the download.

1. Download the installer.
2. Double-click the downloaded file to start the installer. (You may need to look in your browser's downloads folder. The file is named AppInventor_Setup_v_X.X.dmg (where the X.X is the version number)
3. Click continue.
   
4. Read and accept the software license agreement.
5. On the Standard Install screen, click Install. Don't change the install location
   
6. If asked, enter your password to confirm that you really want to install software. Click OK.
7. The installer confirms that the App Inventor Setup package was installed.
   

If you can't install it because it says it's an unidentified developer, hold down the control button, click on your track pad, and then select "open with installer."