Guidance for copying seeded report for customization

Summary:

As someone new to OTBI, I'm hoping to copy a seeded report (Payables Trials Balance Report) to run for specific vendors. I've copied the report, but don't know the data model and subject areas enough to modify intelligently. Is there a How-to, or primer, or even a crosswalk from field name to subject area element that I can use as a resource to get started?
The skill and knowledge to copy a seeded report and customize for ones needs seems like it could be very valuable.

Content (please ensure you mask any confidential information):

Payables Trial Balance Report, and others