Hi kenDonald

Most common used oracle projects tables & views are :

1.PA_PROJECTS_ALL
stores the highest units of work defined in Oracle Projects.

2.PA_TASKS
stores user-defined subdivisions of project work. Tasks can be broken down into multiple levels of subtasks.

3.PA_PROJECT_TYPES
Implementation-defined project classifications that supply default information and drive some project processing.

4.PA_PROJECT_PLAYERS
A multi-org view which will retrive data for your current operating unit and ignore data in other operating units.

5.PA_AGREEMENTS_ALL
Customer contracts that serve as the basis for work authorization

6.PA_BUDGET_VERSIONS
stores the versions of project budgets. There are three categories of budget versions: Draft, Baselined, and Original.

7.PA_BUDGET_LINES
stores the detail information of a project or task budget, including the resource, time period and budget amounts entered. The time period may be PA period, GL period, or any user-defined period.

8.PA_DRAFT_REVENUES_ALL
Stores information about draft revenue generated for projects

9.PA_DRAFT_REVENUE_ITEMS
stores the lines of a draft revenue.

10. PA_DRAFT_INVOICES_ALL
Information about draft invoices generated for projects.

11. PA_DRAFT_INVOICE_DETAILS_ALL
Inter company invoice details for cross charged transactions.

12. PA_CLASS_CATEGORIES
Implementation-defined categories for classifying projects.

13. PA_CLASS_CODES
Implementation-defined values within class categories that can be used to classify projects.

14. PA_EXPENDITURE_COST_RATES_ALL
Cost rates for non-labor expenditure types

15.PA_BILL_RATES_ALL
Information about bill rates and markups of standard bill rate schedules.
 
Note: this is not all the tables and views are available in oracle projects application, however this may help you to get a small insights about what are these tables ? and small description of each one.
 
Regards.