When I click on the download for the mac emulator - nothing happens.
Hello Amanda
Is this the advice and download information you are following http://appinventor.mit.edu/explore/ai2/mac ? Make sure you download the correct emulator for your OS. Both links work properly for me.
Nothing happens? You may have to 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.)