Once your Debian system is running, you can add new features and facilities to it by installing software PACKAGES -- and you'll seldom, if ever, have to restart!
Debian uses a cool packaging system "APT" that takes care of dependencies for you -- package_A may require package_B, which requires package_C, and the Advanced Package Tool will take care of installing package_C and package_B if you request package_A. Very nice!
It's called APT as in Advanced Package Tool.
To see which apt-* commands you have available, you can use a handy feature that's offered by most command shells. (A command shell is the program that interprets your commands and executes your instructions, such as when you type cd or ls or ps. In fact, to find which command shell you're using, that last command will do the trick: ps will list all your processes, including ps itself and your command shell, which is probably bash )
So, try this at your shell's command prompt: type 'apt', and INSTEAD OF pressing ENTER , try TAB instead:
# apt <TAB KEY>
Most command shells will then display for you all the commands that start with those keystrokes. It's a great way to find useful nuggets!
This feature is called 'completion', and most command shells offer it in some fashion.
You can find more details about it in the manpage for your shell: man tcsh,man bash, and maybe others. If you have to press tab twice to get a listing, compare your list with mine below, and then check the manpage and see if you can figure out why it's different... Plus, if completion is not working in your shell, either you or your sysadmin probably turned a feature off. Again, the manpage will help you here.
To see the manual on just about any command, use man, as in:
% man apt-get % man exim.conf % man egrep
See why we call them manpages? :)
On my system, using the tcsh shell, here's what I get:
% apt <^D> apt-cache apt-cdrom apt-config apt-get apt-move apt-setup aptitude %
That is just a snapshot of my system, which is likely to change when I install something else later on this afternoon... (with apt, it's so easy to install stuff, it's nearly dangerous!)
Your system will probably vary, depending on which shell you're using and which packages you have installed, of course.
I'll only talk about apt-setup, apt-get and apt-cache here, plus a bit of a related program, dpkg.