Check out the source code and duplicate what already exists. Don't forget to add new fields to your database and don't forget to change those pages where db info is printed to include your new fields.
I have wanted to do this but I have not had the energy to read all the source and understand it. But, there is no other way, so if you really want to do changes to your site you must learn php and sql and get familiar with the source code.
People wont spend several hours doing the work for you, for free