Session cookies: If you log in, these remember you are logged in. If you add things to the shopping basket, these remember what you have added. Without cookies, you would never be able to log into any website, and a shopping basket would not work.
Persistent cookies: If you add items to your basket in the shop, these are used to remember which items you've added for a set amount of time, even if you leave the website and come back later. They are also used to remember that you are logged in if you select that option.
Cookies are used by almost every website, and they pose no potential threat or harm to you or your computer. If you prefer, it is possible to block some or all cookies, or even to delete cookies that have already been set; but you need to be aware that you will lose some functions of this and other websites if you do.
Find out more here: www.aboutcookies.org