Start by launching the Google Play Store on your Android device.
Next, tap on the right icon for the app and make sure that the app publisher is Microsoft Corporation. This, in turn, ensures that you are downloading the app from the genuine and right source.
Now, tap on Install to begin the installation process of that MS Office application. You may have to accept the license agreement which you can do by clicking Continue.
After some time, depending on your connection speed, the app will get installed. To launch the app, you simply need to tap on the app icon.
Finally, to activate MS office setup, you could enter the login credentials for your Microsoft account. In addition, you might also have to allow a few app-permissions to start using all the features.