Word is Microsoft’s word processing program. It is commonly used for papers, reports, and résumés among other types of documents. Essentially anything you would print out to be read by faculty, colleagues or fellow students can be created with Microsoft Word.
As with Outlook, the Word desktop app has the most functionality and is worth installing if writing is a big part of your scholarship or work.
The following articles from Microsoft's support site should answer most of your basic questions about using the Word desktop app:
If you need additional help using Word, there are many other support articles available from Microsoft accessible from their main Word for Windows training page.
If you want to look at a more thorough training module experience with exercises to work through there are a couple of other options available.
Goodwill Community Foundation Word Tutorial: this tutorial is freely available to anyone with an internet account and offers a pretty thorough introduction to Microsoft Word with a good deal of video content and detailed demonstrations with screenshots.
Learning Word Desktop (Microsoft 365) Online Class | LinkedIn Learning, formerly Lynda.com: This LinkedIn Learning video tutorial can be accessed by Massachusetts residents with a free BLP eCard account.
As with all Office products, the web version of Word is laid out very similarly to the desktop app and functions in much the same way. There are some differences, however, and if you plan on primarily interacting with Word through the web interface, it is worth checking out the documentation specific to it Microsoft has provided: