Which is best or good book or tutorial to understand linux file or directory structure

Here's a much better description of the filesystem. http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/Linux-Filesystem-Hierarchy.html

In every Linux distribution you'll have a man hier man page that describes the filesystem hierarchy :)

In short, /etc is for configurations & admin scripts (those that initialize your system). /var is for variable content in common. /bin is used for common system applications, /sbin are those apps that usually require root (superuser-bin). Also there's /usr/bin for binaries installed by the user.

Cheers! :)

Mirror51, this page gives a good overview.

Each linux distro has some subtle difference from the others, but for the most part, they all adhere to roughly the same file structure.