those URLs starting with deb... are repositories. (like the ones bundled with ubuntu that you access through synaptic)
you can add them under system->systemsettings->paketsources / repositories (or something like that I'm not sure about the english wording)
The second tab should be called third party something there you can add them. Then you can choose the package in synaptic.
Customary warning: third party repositories can endanger you system, because they might contain viruses disguised as system updates.
Those repositories should be trustworthy though.
