Step 1 - Use Apt
The sources.list contains the list of repositories that will be used by the APT application to build up the database of applications that can be downloaded and installed onto the Raspberry PI.
Each line contains a different repository location. Therefore looking at the default sources.list you will see there is just one line as follows:
deb http://mirrordirector.raspbian.org/raspbian wheezy main contrib non-free api
So what does it all mean? Well "deb" is the type of repository which in this case means it is a debian repository. Other types include RPM and Repomd but for the Raspberry Pi running Raspbian we only care about debian packages.
The next part is the location (URL) of the repository.
Following that is the distribution which in our case is Wheezy.
The rest of the items are categories under which applications are based.
You don't need to do anything with this file. This is just a little bit of information which lets you know where APT is getting its data from.
Press CTRL and X to exit.
So the real point of this section is to learn how to download packages using APT so that you can download Synaptic.
The first thing to do is to make sure the APT database is up to date. You can do this by typing sudo apt-get update into the terminal window.
Therefore to search for Synaptic you would type sudo apt-cache search synaptic. This will return a list of packages with Synaptic in the name or description.
In the image above you can see that I have decided to install the Chromium web browser instead. This is because I already have Synaptic installed.
When you use the apt-get install command you will get a message telling you exactly which packages will downloaded and installed and how big they are.
If you are happy to continue installing Synaptic press Y to continue.
When the process is finished type exit to close the terminal window.
On the menu under System there should be an option for Synaptic.
Step 2 - Using Synaptic
You will be greeted by a login window. You will need to enter the password you set up for the pi user and press ok.
Synaptic will load in the background but the message above will be displayed telling you the purpose of Synaptic and package management in general. Notice that there is a "show this dialogue at startup" checkbox. If you do not want to see this message every time you run Synaptic uncheck the box and then click the close button.
Synaptic provides a much more visual way of viewing the packages that are available in the Raspbian repositories.
On the left hand side is a list of categories and on the right the packages that are available in the selected category.
If you want to find a particular application by name or by description click the search button.
A little dialog box will appear. Enter the name of the application or a description of the application and click search.
On the Raspberry PI it takes a little while to search the repositories and progress can be monitored in the bottom right hand corner of the screen in the style of a blue progress bar.
A list of available packages will appear in the right pane which matches the search term.
To get more information about a package click it once with the left mouse button.
A description of the application will appear in the bottom pane.
To mark an application for installation click the checkbox next to the application. You can queue multiple installs by checking boxes next to all the applications you wish to install.
When you are ready to install the application or applications click Apply.
A window will appear showing you which applications will be installed and any required dependencies that will need to be installed as well as the applications you have chosen.
To continue the install click the Mark button.
You get one last chance to cancel the install at this point. The above window will appear showing how big the download is and the list of packages that will be installed. If you are happy to continue click Apply.
A window will appear showing you the progress of the downloads and how long it is expected to take.
When the downloads are complete another window will load showing you the progress of the actual installation.
Finally once all this is done your chosen applications will be installed.