Variables used: s1=A piece of software in the main repo, not included with the main ubuntu install. Preferable a graphical app which the user can SEE working. xchat-gnome maybe? s2=A piece of universe software. How about gnomebaker? s3=A piece of nasty multiverse software. Just to show that you cant see all packages working, lets make this java or rar or soemthing behind the scenes. s4=A piece of main software which isnt installed in the standard ubuntu installtion, but is on the ubuntu alternate cd. apache2?

Before you start, make sure that uni/multiverse are disabled, and you will need an ubuntu alternate CD in the drive. This cd shouldnt be added to sources.list yet.

Log in. State that you want to install s1. Go to synaptic, and point out that there are categories on the side. Also point out how many packages are listed (bottom left of the screen). Now search for s1. Mark it for install and click on apply. Explain whats happening (packages being downloaded, extracted, configured etc). Close/minimise synaptic and demonstrate that s1 has actually been installed.

Open/unminimise synaptic again. Say that you want to install s2. Search for it. It won't be there, becuase universe is disabled. Go into software sources and enable universe, and explain what universe is (not officially supported free software). Remind the user that the number of available packages has increased. Now search for it again in synaptic and install it. Demonstrate that its been installed.

Now say that you want to install s3. Do the same as for s2, but enable multiverse, and say that its non-free software, restricted by copyright etc etc. If you can demonstarte that its working (eg if you used unrar, you can show by opening a rar archive), do. But if you cant, dont worry.

Now search for skype in synaptic. It wont be found. Say that this is because its not in the ubuntu repos, and you need an extra repo. Go to http://skype.com and go to the download page. Point out that theres a deb package, which you could install, but then it wouldnt be updated as new versions are released. Click on the repositories link. It will give you this line:

deb http://download.skype.com/linux/repos/debian/ stable non-free

Say that this describes where ubuntu can get software and updates from. Point out that extra repositories such as the skype one arent officially supported by ubuntu. Add it using the 3rd party tab in software sources. Rename it to Skype. Go back into synaptic and install skype. Open skype and show that its installed.

Go into software sources and un-check all of the repositories, and disable (but dont delete) the skype one. Explain that this is what it would be like if you had no internet connection, and that you've told ubuntu not to get any software from the internet. Add the ubuntu alternate cd thats in the drive. Go back into synaptic and point out that the number of listed packages has dropped a lot, becuase you cant fit much on a cd. Search for and install apache2.

Decide that you dont want s1 any more. Remove it using synaptic and explain/demonstrate that the software's now gone. Decide that you dont want s2 either. Purge (completely remove) this using synaptic. Explain/demonstrate that no only has the software gone, but the configuration files have gone too.