The Linux filesystem is organised as a single directory tree starting at /, called the root directory. Other disks and partitions are mounted somewhere inside this tree.
/
/ is the top of the filesystem. All files and directories appear below it, even when they are stored on different disks or filesystems.
/home
/home usually contains user directories, such as /home/gaurav. Personal files, shell configuration and user data normally live here.
/etc
/etc stores system configuration files. Many server and network settings are configured through files in this directory.
/var
/var stores variable data such as logs, caches, mail spools and application state. Server logs are often found under /var/log.
/bin, /sbin and /usr
These directories contain programs, administration tools and shared system files. On many modern distributions, some of these paths may be symbolic links into /usr.