It is a beast of a tool. I still only use a tiny fraction of it's potential. I use it to spot Trends, which are the right hand side of the dashboard (its the current most searched for keywords on etsy - 2 weeks ago it was "trump mugshot"). Then in the main portion of the dashboard, it summarizes my shop (inventory, missing/unoptimized tags, missing images, sales to date, global and national ranking, a few other less useful stats).

When you sign up, you connect your shop to your profile. After that, you can look for competitors and add them for comparisons.