When you add your domain to Monitor Backlinks, the site shows you the Competition page, and the next page leads you to add the keywords you want to monitor.
The tool already includes keyword suggestions that you may wish to watch over based on your Google Analytics data. You may or may not already be ranking for the suggested keywords in Google:
There’s a good chance that you’re already driving traffic from the suggested keywords, so you might as well track them.
You can remove the suggested ones later on if you need to anyway.