In url type office.com/setup in your favorite browser.
Sign in to Microsoft account and create a new account.
Now Enter your 25 digit office setup product key.
Then you need to go according to your plan and version.
If you have a work or school account, click on install Office Apps.
Click on download button.
Office setup file will get downloaded in few minutes.
Double click on the file to run and install office.
Follow on screen prompts.
Click agree on terms an conditions.
Wait to complete the installation of office setup.
Open any office application such as excel, word then Click on activate button.
You need to sign in or enter product key.
Enter office setup product key.
Click on activate button so Microsoft office will be activated.
Restart your device and enjoy office subscription.