Oracle is one of the leading enterprise software firm. Major ERP applications of Oracle include Oracle Fusion Application, Oracle E-Business suite and PeopleSoft enterprise. ERP stands for Enterprise Resource Planning. The ERP software from Oracle consists of Modules which are integrated to one another and "talk " to each other.
The major modules include
Oracle Purchasing - This module handles purchases and requisitions.
Oracle Accounts Payables - It is used to integrate payments to be made to vendors.
Oracle Accounts Receivables - It integrates all the payments due on account of the deliveries made to the customers.
Oracle Order management - This module helps in keeping track of the orders received via different channels.
Oracle Human resources -This module maintains the personnel activity of the organization.
Oracle general Ledger - This module collects information from all the other modules and summarizes them so that you can create a profit and loss account, Tax paying reports etc.
In addition, Oracle also has a sleuth of modules like Oracle inventory, Oracle Cost management etc.
This is just a layman's explanation to what is Oracle ERP and how it works. The exact functioning can only be understood once you get proper training on the subject which is beyond the scope of this response.