Hypertext transfer protocol (HTTP) does not preserve state. Your browser sends each request to the server independently. Cookies allow browsers to preserve state. For example, this site uses a session cookie. When you log in, your browser creates a file that it sends the next time it requests a page from this site. When the site sees that session cookie in the request, it knows that you’ve logged in as a member, so it can send you members-only functionality. If you try to edit an encyclopedia entry without that cookie, the site will return a 401 code, telling your browser that you don’t have permission for that. If you try to edit it with a session cookie, you’ll get the form to make whatever changes you would like to make.
We do not use any of the information we gather for marketing purposes (unless you count making the site easier and more useful as marketing), and we’ll never sell your information to anyone.