They are the name of small amounts of data that are sent from a website to your browser and stored on your computer's hard drive. Your browser's preferences usually have 'cookies enabled' (meaning each website can send its own cookie to your browser). Cookies cannot access your personal information, but instead use anonymous unique identifiers.
Cookies need to be enabled on your browser to allow you to add product(s) to your cart and access your account information. If you are using a public computer, or share your computer with others, be sure to log out before leaving your computer unattended to protect your account information. You can log out by clicking the 'Logout' link in the top right hand corner of the page.