Identification and Authentication
Before a customer can shop on a transactional website, it is often necessary to log in or register. This involves giving information that uniquely identifies the customer such as name, email address etc. 

The website server will then be able to keep a record of the customer's shopping history.

It is important that the server dealing with the customer's shopping basket does not get mixed up with those of other shoppers.

Often, a cookie is placed on the customer's computer.

A cookie is a small file containing information that identifies the customer. It will allow the transactional website's server to identify the customer, and view any preferences the customer has made (Eg the language used).