Firstly, you have to open and office365 app in your system.
Next you have to click on activation button.
Click the Next button.
When you open it, click ‘Accept’ on the license agreement.
Enter the 25 digit Office Setup Product Key in the space provided.
Now you have to login to your MS office account for activate MS office.
If You don't have any ms office account.
Then firstly you have to create one at office.com/setup.
After Create an MS office Account you need to login.
Now Restart your system after following the given instructions.
When the activation completes, select ‘Close’ in the end.
Your Microsoft Office is now activate .