file systems
 

my doubt is, the "/", the swap, the /var and the /usr are the different filesystems or what ?
because I read somewhere that, / is on the top and every other file system can be mounted under this partition.

if the above lines are correct , then where the ext3 or ext4 file systems are ?

ext3 and ext4 and a number of others are file systems for managing communication between the OS and the physical drive.

/, /etc, /usr, and so on are part of the file structure on that drive.

The Slackbook has a nice explanation of the file structure:

http://www.slackbook.org/html/book.h...URATION-LAYOUT