Microsoft Word, or MS Word as it’s called in the title, is a typing tool. It’s a word processor (that’s the typical term used to describe something like this), and it has a few tools integrated into it that allows many kinds of professionals to use it for their job. There is a spell and grammar checker; the red lines are spell check and green and blue are grammar checks.
MS Word is something that you can use without internet access, so it has a few advantages over online word processors right there. There is also a dictionary and thesaurus function included in the latest version of Word; these functions can also be used offline, in case of an internet outage.