There are two types of JavaSript cookies- permanent, and session-only. The first one stores its information in a physical file on the client's computer called "cookie.txt", with the stored data "permanently" available. Session only cookies, on the other hand, stores information in the browser memory, and is available for the duration of the browser session. In other words, the data stored inside a session cookie is available from the time of storage until the browser is closed. Moving from page to page during this time does not erase the data.
This tutorial, as mentioned, focuses on session only cookies. Empty your stomach as we dive into em'!