This download is an XAPK file.
To install, you will need to download one of the following apps:
XAPK Installer - Open the app, and it will scan your device for any XAPK files. Installation is as simple as tapping your screen.
ZArchiver - Open the app and browse to where the XAPK file was downloaded. Tap on the file and select install.

It will be much simpler for the average user to click the Google Play link and download from there.