Unfortunately, it means pretty much what your pattern says it means. Have you read through the pattern completely? Sometimes such things are included in a Stitch Key or Terminology section. Take a look through the entire pattern and see if you can find anything that explains what they mean by "sets".
Also, if you have a link to your pattern, someone might be able to look it over for you on line and figure it out for you.
But whatever you do, don't give up!