A shopping cart is a software application that typically runs on the computer where your website is located (the Web server), and allows your customers to do things such as searching for a product in your store catalog, adding a selected product to a basket, and placing an order for it.

The shopping cart "integrates" with the rest of your website. In other words, there are typically links on your Web pages that customers can click on, and which allow them to perform some of the functions described above; For example, many ecommerce websites have a "search" link appearing on every Web page, as part of the navigation area. The link will point to a feature, such as the search feature, provided by the shopping cart.

Shopping carts are written in a variety of different programming languages. Some of them provide full access to the "source code", thus allowing experienced programmers to make modifications to the system features, some others do not. Some shopping carts run on Windows Web servers, some on Unix, others on both. In most cases, you can place the shopping cart on your Web server simply by transferring its files there using any FTP software, where FTP stands for File Transfer Protocol.

More simply put — primarily a shopping cart has three tasks: keeping track of all the products a customer has chosen to buy, tallying the total cost of those items together, and receiving payment for those items at checkout. Some of the more advanced carts will have extra features such as inventory management, shipping cost calculators, digital downloads, affiliate tracking, and other features.

Anyone who runs an online business where more than one product or service is sold should have a shopping cart; anyone from a merchant selling dolls on a small scale to Amazon.com. The decision of which cart to buy is up to the individual business, but anyone who has a product or service to sell will quickly recognize shopping cart software is the best option for taking orders and receiving payment.