Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
There is no free version of Office 2016. If you purchased it in the past, you can (re-)install from your associated account.
An alternative to Microsoft Office would be to try the open source office suite called LibreOffice. It includes a word processor, a spreadsheet program and a presentation program, and it can create files that are compatible with the Microsoft Office counterparts.