First You had to Tap on the Download Button to Get the Download Process Get started
Once you click on the Download button the Downloading Will be started. You have to Wait Until the Downloading Will be finished.
When the App is Downloaded in your Mobile Phone then you are ready to Install. You simply have to Head over to the Download section of your browser and tap on the Apk File you Downloaded.
Installation will be started as Soon as you clicked on the App.
Depend on the Android Operating System version you are Using in your Phone, It may ask you enable the Installation from Unknown Sources in process of finish the Installation. You had to Allow it.
Once the App is Installed you have to Click on the Done. Now you can Open the App.