Download FREE iPhone or Android App
Most Android devices don't allow the installation of apps from other than Google Play. Downloading from here is considered one of "unknown sources". Fortunately, it's usually very easy to enable this functionality.
Simply pop over to your phone's Settings menu (usually found by hitting the menu button from the home screen), and tap the option for Applications.
You should see an option that says "Unknown sources." Check the box next to it, then click OK on the resulting popup alert.
Unfortunately, not all Android devices will offer this option. Most notoriously, devices offered by wireless carrier AT&T have locked users out of enabling unknown sources. In this case, please download from Google Play.