When I first started using linux, the names of the folders confused me. I didn't know what they were used for. So I wrote this little guide to help new users (and because I was bored ).
All of the following directories are located in '/'
bin - Usually holds commands and shells
boot - This is usually where the kernel, grub/lilo (if you use them) are
dev - This holds device files, device files are files that represent devices. For example, /dev/dsp is a sound card, /dev/cdrom is your cdrom. So any data writen to the /dev files get directed to their corresponding device. If that isn't accurate please tell me!!!
etc - System configuration files
home - Where a regular users home directory resides.
initrd - This will explain it much better than I can - http://sial.org/howto/linux/initrd/
lib - Libraries. Kernel modules and things needed to run commands. Libraries are like .dll's in windows.
lost+found - fsck (filesystem check) puts unreferenced files it find into this dir
mnt - Mount points for drives other than '/'. Like your cd and floppy as well as network drives.
opt - Optional software
proc - Gives information about devices. Try a 'cat /proc/cpuinfo'
root - root's home, it's because some people put /home on a different partition, and if that goes boots up, root will need to do some administrating
sbin - Commands/programs that need root access
tmp - For temporary files.
usr - Programs, man pages, libraries, just about everything is in here.
var - Variety. It's for files that change often like logs.
Hope that helped someone.