The NPRM describes where and when comments may be submitted, where and when you can review comments others have made and how to respond to those comments. The Petition is acted upon by the Commission. Everybody can get involved in the comment period. You don't need to be an attorney or hire one. Each of the documents detail how and where comments can be filed.
Comments are just that.
You tell us your feelings about the subject topic. Reply comments also are what their name implies. You can review what others say, and then support or disagree with a point and file a reply comment. We are often asked who sees the comments. Well, for one, the Commissioners and staff.