To install Office 2016 for Mac, you must first visit the Microsoft website and sign in with your Microsoft account. If you don't have one, you'll need to create a Microsoft account here.
The Microsoft website can be found here.
After you have logged in, you can enter the product key we received, follow the instructions of the installation manager and download the installation file.
Once the file has downloaded, double-click the installation file to start the installation and follow the instructions.