Check out this article
. It explains some basic concepts of Linux in terms of Windows concepts.
Keep in mind that Linux is based on Unix which was used for large systems, i.e. systems with many users. Also keep in mind that this was when 20 MB was a BIG hard drive. So the old school unix programmers had to split up the drive usage for the large amount of people and the directories became the mount points. This also allows other computers to use the same mount point. For example, the mail server writes to /var/mail and each of the other computers in the network can then mount that directory as its own /var/mail. Otherwise each computer would have to download the mail or the server would have to send the mail to each computer; either way it's just easier to mount the network drive. Hope that helps a bit.