It shouldn't be hard.

The site works something like this:

1. I post a Family Circus Comic, trimmed of its caption.

2. You send me an email at familycirclejerk@outlook.com with a subject line something like "Caption for comic X" and the body containing your caption and preferred name to be credited under. Alternatively, post your submission in the forum, under On-topic > FCJ Submissions.

3. The caption will be reviewed and, if deemed usable, posted to the according comic's page.