I am sorry, but I think your question is a little too broad to answer.
It sounds like you need to maintain a site, and the site has custom modules that it uses.
It also sounds like maybe you are interested in knowing how to go about testing new changes you intend to make for the site.
If all of this is true then I think you need to learn Drupal first.
This page should get you started: http://drupal.org/documentation/develop
You may also want to look at the Devel module: http://drupal.org/project/devel
If you have a little more specific details let us know so we can help you out.