Red underlines: When you're typing, Grammarly shows any suggestions it has with a red underline.
If you hover over the underline, it shows the suggested correction. You can accept or reject Grammarly's suggestion in each instance.
The Grammarly icon: When you're in a Google Doc with Grammarly enabled, there is an icon in the lower-right corner.
This icon tells you information at a glance. When the icon displays a spinning wheel, Grammarly is checking your work.
If the icon is green, Grammarly does not see any issues with your writing. When the icon turns red with a number inside it, that means Grammarly has identified some issues.
The Grammarly sidebar: To see an in-depth list of suggestions, click the Grammarly icon, which opens the Grammarly Sidebar.
You can see the edits in the sidebar, and clicking a suggestion gives a more in-depth description of the edit.
Goal setting: Grammarly allows you to set goals for your writing. You can set goals for the audience, formality, domain, and intent of your piece.
Each goal has different options depending on if you're a free or premium subscriber.