Grammarly has recently partnered with specific websites and apps, allowing users to check writing while in their service—saving users time by having all writing suggestions directly in-app! If you’re seeing a Grammarly button and have not downloaded the Grammarly browser extension, this may be why!
The Text Editor SDK checks your text as you write within a specific text field and provides writing suggestions.
When you click into a text field, you should see Grammarly’s logo in the lower-right corner. As you start typing, Grammarly will begin to check your text dynamically.
Grammarly’s suggestions in the text field should appear as underlines. To accept a suggestion, hover over the underlined text and click on the suggestion that appears: 
If you are a developer looking to integrate Grammarly into your website, check out this page for more information.