Important Note: Please make sure your device allows installation of apps from unknown sources.
Enabling 'Unknown Sources' on Android
The exact names of the settings entries listed below may vary slightly from device to device, but the overall process should be very similar. To begin, head to your phone's main settings menu, then look for an entry titled either "Security" or "Lock screen and security."
From this menu, simply tick the box or toggle the switch next to the "Unknown sources" entry, then press "OK" on the popup.
Now you can proceed with downloading and installing the app (See above).