Partner Processing 
Partner processing controls how the system works with business partners in transactions. It ensures the accuracy of partner data in transactions by applying rules you specify in Customizing, and it makes your work easier by automatically entering certain partners and related information, like addresses.
One of the most important aspects of partner processing is partner determination, the process by which the system automatically finds and enters the partners involved in a transaction. In most transactions, you manually enter one or more partners, and the system enters the others through partner determination. Various sources of information make partner determination possible; two of the most important are business partner master data and organizational data.
Example
A user creates a sales order, and enters the name of the sold-to party. Immediately, by checking the master data of the sold-to party, the system enters other required partners, such as the bill-to party, payer, and ship-to party. By checking the organizational data, the system enters the employee responsible for the region where this sold-to party is located.
The following figure shows this combination of the user's entry and automatic partner determination.
Prerequisites
You have maintained business partner master data, organizational data, transaction types, and item categories.
You define transaction types and item categories in Customizing
for Customer Relationship Management, by choosing 
Transactions 
Basic Settings
Define Transaction Types/Define Item Categories
.
Features
With Partner Functions, you define partners with the terminology used in your area of business and in your company. For example, if you have a real estate business, you might define the partner functions Tenant and Mortgage Provider.
In Access Sequences, you specify the sources of data the system uses for automatic partner determination, and the order in which it checks those sources.
In Partner Determination Procedures, you specify which partner functions are involved in a transaction, assign access sequences to the functions the system should determine automatically, and set other rules for working with partners in transactions.
With Partner Teams, you define groups of partners involved in an individual project, or even in a single transaction. Partner teams are used in opportunity management.