Cookies are small text files that many web sites store in the devices users use to access the Internet, to identify individual devices that are used to access it. Their storage is under the full control of the browser used by the user - he/she can store cookies optionally, or restrict or disable them.
Cookies are therefore nothing new; all website visitors have already a lot of cookies stored on their computers, tablets and mobile phones from various websites. What is new is only the legislation (the Electronic Communications Act-1), which leads to changes in informing and consenting visitors with their use. If you turn off cookies, some options of the website might be disabled.
By themselves, cookies are not harmful; they do not contain viruses or any other malicious code. They are used for various purposes for meetings (e.g. logging in to forums), for baskets in online stores, to display various advanced facilities for conducting statistics of visits to support a plug-in to social networks, and also to show ads tailored to the user online.
How to manage cookies in your browser