A cookie is a small text file that a website saves on your computer or mobile device when you visit the site. It enables the website to remember your actions and preferences (such as login, language, font size and other display preferences) over a period of time, so you don't have to keep re-entering them whenever you come back to the site or browse from one page to another.
When someone browses the website, anonymous site usage information is collected via various technical means. The usage of the site is recorded in log files. These files contain no personal information, nor information about which other sites the visitor has browsed. They allow to improve the service by knowing its usage, and are processed anonymously.
You can control and/or delete cookies as you wish - for details, see AllAboutCookies.org. You can delete all cookies that are already on your computer and you can set most browsers to prevent them from being placed. If you do this, however, you may have to manually adjust some preferences every time you visit a site and some services and functionalities may not work.