Q: how to use my Mac book

Word is an application in Microsoft's Office software which you can purchase and install if you follow this link:

http://www.microsoft.com/uk/mac (you can change the country if necessary).

However, if your Mac is brand new you should be able to download for free from the Mac App Store (in the Apple menu) Pages, Numbers and Keynote - programs that are not equal to the power of Office but certainly meet many users needs. No harm in trying them first - it may save you needing to buy Office.

You'll need to log in to the Mac App Store with your AppleID.

https://www.apple.com/creativity-apps/mac/up-to-date/