/etc contains all your config files. It's kinda like a text only version of the Windows registry (or not) It determines how your system gets setup. Linuxconf is just a program that edits the files in /etc. If you want to learn more about what's in /etc, type "man fstab" or "man smb.conf" or whatever file you like. Most of them have man files.
/dev is a list of your devices. Actually, this is a list of all possible devices so don't think you actually have that many. Most of the /dev files aren't used. I wouldn't go deleteing them at random though.
/usr is kinda like the Program Files directory. It contains all your programs, usually in the /usr/bin, /usr/sbin and /usr/local/bin directories.
/home is kinda like the My Documents directory. It is your personal directory (assuming you've made a real user besides root). It also contains personal settings so it's really more like the NT WinNT\Personal directory.
/bin and /sbin contain system files.
/opt and /var are other locations for programs. /var/lib/apache is your webserver usually and /var/lib/X11 is your X server (on some systems)
/boot and /proc are your current system settings. The files in these directories don't really exist (I think). They are defined by the current state of the system through a special device (/dev/md maybe??)
/include, /lib, /usr/include, /usr/lib, /usr/local/include and /usr/local/lib are used for programming and as loadable modules (kinda like DLLs) by existing programs and the OS itself. Many device drivers, like your net card, are loadable modules. These directories amount to your Windows\System and Windows\System32 directories.
That's just a quick look. Any good book on Unix will explain the directories and files better than I can.
