Microsoft for Mac

If you don't have Microsoft Office already, you can either subscribe to Microsoft 365 or you can make a one-time purchase. See: https://products.office.com/en-us/buy/compare-microsoft-office-products-for-mac?ms.officeurl=mac-compare-redir

If you already have an early version of Office for Mac 2016, you can update it at no charge. However note that connecting to Microsoft 365 services using Office 2016 for Mac is not supported by Microsoft after October 13, 2020. See: https://docs.microsoft.com/en-us/office365/troubleshoot/administration/office-2016-for-mac-64-bit-upgrade

If you alreadyhave Office for Mac 2011 or earlier, that is not upgradable. You can either subscribe to Microsoft 365 or you can make a one-time purchase. See: https://products.office.com/en-us/buy/compare-microsoft-office-products-for-mac?ms.officeurl=mac-compare-redir

If you don't want to subscribe or buy Microsoft Office, there are other options that are free:

You can use the free Microsoft Office on the web: https://products.office.com/en-us/free-office-online-for-the-web

Or Google Docs: https://www.google.com/docs/about/

Other options include using the free and very good Libre Office https://www.libreoffice.org/

or Apple's Pages and Numbers