Office 365 for Mac

Microsoft 365 (as it is now named) is subscription based, and you can install it now on High Sierra, but once Apple finally releases Big Sur (macOS 11) this Fall, Microsoft will then require macOS Mojave for installation of any Office product. There is also a single-purchase, Office 2019 for Mac at $150 for home and $250 for Home & business versions.

The Microsoft Office applications found in the Mac App Store are strictly Microsoft 365 subscription-ware. Apple offers the Microsoft 365 subscription plans, and single-purchase Office 2019 for Mac through the online Apple Store.

cindyhuie wrote:

what should I know before downloading Office 365 for Mac

What don't you know? How could we possibly know what you should know?

Maybe start here then look on the Microsoft site for Office Help and Support Communities.

Look into the Free LibreOffice, it handles MS Office files like Word & Excel…

https://www.libreoffice.org/