Linux has a directory structure which can be a little confusing. Here’s a basic description of it.
/ – the root directory
/bin – binary executable commands like ls
/boot – the linux kernel and stuff for the linux loader and grub
/cdrom – permanent mount for cdrom
/dev – attached devices like serial ports
/etc – miscellaneous configuration files and initialization scripts for the system
/home – the home directories for all the users of the system
/lib – library files for programs
/lost+found – lost files
/media – folder for mounted media devices. The cdrom can be mounted here, but is usually the /cdrom directory now
/mnt – folder for temporarily mounted devices
/opt – storage for large programs
/proc – running process information
/sbin – executable commands used for administration and so more secure
/srv – internet server information
/sys – linux kernel system devices information
/tmp – user available temporary directory flushed when booting
/usr – sub-directory for online manual
/usr/X11R6 – X Windows System
/usr/bin – an extended user collection of executable binary programs
/usr/lib – extended user library collection for C and C++ programs, Python programs, etc.
/usr/local – this is where binary executable programs should be that you compile yourself
/usr/share – shared data for programs among all users. A lot of configuration files for applications will be here.
/usr/share/man – the manual/help files for your system
/usr/src – the source code for the linux kernel
/var – various system files including logs and files for a web server or FTP server
/var/cache – cached data for programs
/var/lib – information for current program states
/var/lock – locked files so a file is only used by one program at a time
/var/log – log files
/var/mail – mailbox
/var/opt – variable data for packages
/var/run – data since booting
/var/spool – spooled data
/var/tmp – temporary data preserved between booting sessions
/var/yp – files for NIS (network information service) database