Shopping cart software is software used in e-commerce to assist people making purchases online, analogous to the American English term 'shopping cart'. In British English it is generally known as a shopping basket, almost exclusively shortened on websites to 'basket' or 'cart'.
The software allows online shopping customers to place items in the cart. Upon checkout, the software typically calculates a total for the order, including shipping and handling (i.e. postage and packing) charges and the associated taxes, as applicable.

These applications typically provide a means of capturing a client's payment information, but in the case of a credit card they rely on the software module of the secure gateway provider, in conjunction with the secure payment gateway, in order to conduct secure credit card transactions online.
Some setup must be done in the HTML code of the website, and the shopping cart software must be installed on the server which hosts the site, or on the secure server which accepts sensitive ordering information. E-shopping carts are usually implemented using HTTP cookies or query strings. In most server based implementations however, data related to the shopping cart is kept in the Session object and is accessed and manipulated on the fly, as the user selects different items from the cart. Later at the process of commit, the information is accessed and an order is generated against the selected item thus clearing the shopping cart.
Although the most simple shopping carts strictly allow for an item to be added to a basket to start a checkout process (e.g. the free PayPal shopping cart), most shopping cart software actually provides additional features that an Internet merchant uses to fully manage an online store. Data (products, categories, discounts, orders, customers, etc.) is normally stored in a database and accessed in real time by the software.

The items you are interested in buying go in this cart and when your ready to checkout you can view and choose the items on which to buy on line:)

They are virtual shopping containers that log what you select, that's it.