The content of the cookie file is mostly determined by the web server it came from. In the cookie file, Internet Explorer stores the exact URL the cookie came from, the expiration date of the cookie, and maybe a few other details. The rest of the data are whatever the web server asked your browser to store. Sometimes it is human readable but usually not. Netscape Navigator takes a slightly different approach to storing cookies.
All cookies are stores in one file named cookies.txt.
In this file, each cookie is stored on a separate line. You probably know that a single web page is usually made up of many separate files. The main part is an HTML file called something like Index. That file just has text and some formatting commands. Images and animation are stored in separate files such as .JPG and .GIF files.