In American homes, or so the story goes, when visitors arrive they are given a cookie which in Britain would be a biscuit. This philosophy has now been extended to the Internet. Whenever a visitor, better known as a Browser, arrives at certain sites a cookie is sent down the line and saves itself to the local computer's hard disk.
There is nothing mysterious or dangerous about this. All it means is that there are certain sites which ask for personal or company details before they allow access to the website proper. This can be either to collect marketing information, visitor statistics or even to restrict access to those sites offering a premium rate service which could be anything from stock quotes to hard core pornography. Anything is possible, but the point is, having entered those details once, it would be tedious beyond belief if a regular user had to constantly enter those same details every time they visited the site. In other words what was wanted was a system whereby the details could be entered only once and then transmitted automatically every time the website was re-visited - otherwise known as a cookie.
A cookie is nothing more than a very small text file containing whatever information that particular website needs to allow the user access. They are not dangerous, they cannot harm the computer in any way and they even come complete with an expiry date. All they do is automate what would otherwise be a time consuming, and annoying, operation.
Obviously from the point of view of a web designer they can be a valuable tool which is why they are mentioned here, but, that apart, there is nothing to think about. If a particular website would benefit from being able to create its own cookies the web designer will mention it, if not they are just a curiosity of Internet life which can for the most part be safely ignored.