One of the largest hurdles with learning Linux is always the directory structure. While not complicated it is very different from any Windows based operating system which is where most new Linux learners come from. Here's a quick explanation of the most important directories on a Linux distribution.
/bin - This directory contains most of your non-privileged system commands such as ls, mkdir, rm, etc.
/boot - Contains the systems boot image, bootloader, and the kernel
/dev - Symbolic links to system devices such as optical and removable drives
/etc - Contains all system configuration files and most configurations for installed packages
/home - Contains a directory for each user and contains profile information
/lib - Contains dynamic libraries and modules for the Linux system and installed packages
/media - Contains mount points for optical drives and removable media
/mnt - Used as a location for mounted drives and shares
/opt - Contains user installed packages and custom software not handled by the system or package manager
/proc - An interface between the kernel and the system, useful for diagnostics and system information
/root - The root superuser's home directory
/sbin - Contains privileged commands that are usually run as superuser (root/sudo)
/sys - An interface between the kernel and the system, used for modifying system settings
/tmp - A location for temporary files such as sessions on a web server
/usr - Contains most installed packages that are not part of the system, user installed programs
/usr/bin - Contains commands related to user installed packages in /usr
/usr/sbin - Contains privileged commands related to user installed packages in /usr
/var - Contains files that change often or accessed frequently
/var/log - Contains all system logs and most logs generated by installed packagesThere are more default directories on a fresh Linux install but these are the main important locations. Please take special care when interacting with the /boot or /sys directories as a small error could make the system unstable or unable to boot.