The tool opens the heuristics in a side panel next to the website you enter. You select a problem area on the screen, related to one of the usability heuristics and a callout appears for you to add notes and recommendations. When you're done a report is available with screenshots and your notes for each issue. You can download the report as HTML or in Word .docx format.
Looks like a nice tool for evaluating web sites in Chrome, as long as the pages you're reviewing have selectable DOM elements.