Settings > Security > Unknown sources
Navigate to Security within Settings and enable applications to be installed via unknown sources. Depending on your Android version, you may need to select 'More' tab to view security options.
This allows you to download apps from sources other than Google to your mobile device. You should take care to download content only from sources that you know (such as Sky Vegas).
Notifications > SkyVegas.apk
Swipe down to view notification centre and select skyvegas-1.0.apk
You are now ready to use the app. Open the app to ensure it has installed successfully.