When you're writing a lot, whether for your education or profession, it's easy to make mistakes, whether they be typos or straight up grammar errors. One of the more popular services to catch problems or offer suggestions for writing improvement is Grammarly. There's already a Chrome extension for it (in addition to the dedicated editor), but now all users will be able to get writing help right in Google Docs.
This feature is in beta for now, but it's rolling out to everyone starting today. All you need is the Grammarly Chrome extension and you're set; just open up a Doc and you'll see the logo in the bottom right corner. Suggestions will be marked with a red underline, with more details available if you click on the piece in question. Bear in mind that if you activate Grammarly for a very long document, it will ask if you want it to read the whole thing, which might take some time.
Grammarly says that this feature is rolling out over the course of the next month, starting today. Just be sure to have the Chrome extension installed.