if something goes wrong.

Clearly there are many more directories on the system - far too many to
describe every one.

For changing things, you'll usually want to confine yourself to your home
directory and /etc. On a Debian system, there's rarely an occasion to
change anything else, because everything else is automatically installed
for you.

/etc is used to configure the system as a whole. You'll use your own home
directory, a subdirectory of /home, for configuring your own preferences
and storing your personal data. The idea is that on a day-to-day basis,
you confine yourself to /home/yourname, so there's no way you can break
anything. Occasionally you log in as root to change something in a
system-wide directory, but only when it's absolutely necessary. Of course,
if you're using Debian at a school or business and someone else is the
system administrator, you won't have root access and will be able to
change only your home directory and any other directory that you own. This
limits what you can do with the system.

File Compression with gzip

Often it would be nice to make a file smaller - say, to download it
faster, or so it takes up less space on your disk. The program to do this
is called gzip (GNU zip). Here's how it works:

$ cd; cp /etc/profile ./mysamplefile
This switches to your home directory and copies an arbitrarily chosen file
(/etc/profile) to your current directory, in the process renaming it