Once you have downloaded and installed the subscription package of Microsoft Office, then you need to activate it via the Office link www.office.com/setup.

Below are the complete instructions to activate the product completely:

First and foremost, hit the start tab.
Then, reach the Office site at office.com/setup.
You have to double-tap on the MS Office file there.
After a while, a link for activation will appear, and you have to hit the My Account tab.
Now, press the My Subscription section.
Type the product key into the required bar.
After a while, the Office subscription will activate on automatically, and a confirmation prompt will appear on your device screen.