If SAP DB is new to you, we recommend that you first read the manual The SAP DB Database System.
This manual will give you an overall idea of the SAP DB database system, its architecture, user and security concepts, database tools, the directory structure, important database parameters, the data management architecture as well as an overview of the available documentation and relevant database terms.
A second source of general information is the Reference Manual: SAP DB 7.4. This document outlines the syntax and semantics of the SQL statements for performing operations on the SAP DB database system.

SAP has several layers. The Basis System is the heart of the data operations and should be not evident to higher level or managerial users. Other customizing and implementation tools exist also. The heart of the system from a manager's viewpoint are the application modules. These modules may not all be implemented in a typical company but they are all related and are listed below:

For performing any kind of task in the SAP R/3 ERP system, a transaction is used. SAP provides a standard set of transactions to manipulate i.e insert, update, delete and display data in the system. But sometimes, the need to create a customer specific transaction may arise due to the following reasons
Standard SAP may not support that task
A particulartransaction needs to be customized to suit the customer requirements.
A transaction is defined as a sequence of dynpros (sap term for screens) having input and output fields and corresponding processing logic behind them to perform a particular task.

SAP based the architecture of R/3 on a three-tier client/server model.
Presentation Server
Application Server
Database Server

Presentation Server

In order to understand a system like SAP a thorough understanding of the events and relationships that take place in a business is required. It is not enough to just realize the Sales, Production, Finance and Accounting have jobs to do in a business. The exact details of each action, the timing of that action and its interrelationships with every other process must be understood. In many large operations there may be no person that has a complete grasp of the situation. Before an operation can be automated or computerized a thorough study of the business must be undertaken. This task is called Business Process Engineering.