As ljp noted, if it is the specific error, check the PDK documentation. Calibre provides the tools, but the PDK creator defines what is actually being checked.
If it is how to use the Calibre tools, open the "InfoHub" version of the documentation (from a Calibre GUI, it should be under the Help menu). This will open in a browser; on the left nav, find the "Videos" tab. It lists a bunch of introductory videos. If the problem is in locating the spots in the layout corresponding to the errors, you probably want the videos that mention Calibre Interactive or Calibre RVE. (The video series is also packaged as a PDF in the pdfdocs directory: calbr_gs.pdf. Can't recall if those videos play locally or take you to Mentor's Support site, though.)