The filesystem and moving around

Linux has no C: or D: drives. Everything grows from a single root, /. Disks, flash drives, and network shares are attached (mounted) inside that tree as ordinary directories.

A few important places:

/home    user home directories
/etc     system configuration
/var     changing data: logs, queues
/tmp     temporary files
/usr     installed programs and their data

Three commands hold the whole of navigation:

$ pwd            # prints the path to the current directory
$ ls             # shows the contents
$ cd /etc        # changes into a directory

ls has useful options: ls -l gives details (permissions, owner, size, date), ls -a shows hidden files,