Yeah, I sat it that form for over a year, working up to fill it out!
If you have had the form for a while, check the USCIS website as there is a new form recently. Not sure that it matters, but I think the newer one is clearer to fill out.
The first part asks for information about you - the petitioner. Part 2 asks for "Data for Identification of Personal Records" - your child.
Under "Specific Information About Desired Documents or Records" I put " Any and all documents pertaining to the adoption and/or immigration of (child's full Guatemalan name with your last name as on B/C) including, but not limited to, foreign adoption and birth records, visa and immigration records, photos, and any other documents contained in the file of USCIS." (You have to write REALLY small!)
Then I signed the bottom and there is a second page to have your signature notarized.
I included a copy of my child's Guat passport and CofC for their proof of identity, and a copy of their Guat birth certificate as my proof of identity as parent. Some people have told me then sent in a copy of their driver's license as well to prove their identity.
Since I only mailed it on the first and haven't gotten anything back yet, I can't be sure I did it right, but at least they haven't returned the form to me!
There is no cost except what it costs to have it notarized.