very confused about getting my photo onto craigs list imac g4
Need more information as to what, exactly you are doing and what software you are using.
If all you want to do is to post a photo from your iPhoto app onto Craigslist, simply select the photo in iPhoto, either drag it to the desktop or use the export functon to export to the desktop (doing this will allow you to choose the size of the photo), and then upload to Craigslist from there.
Does that answer your question? If not, please post back with more info and we can help from there.