Gnome Shell vs Gnome Desktop Environment

I have just installed Ubuntu 12.04, after having been on 10.04 for a long time. I don't care for the Unity desktop and intend to install Gnome.

I have several questions regarding the new setup:

(1) What application do I use under 12.04 to install software? Apt? Synaptic? Do I obtain these apps from Ubuntu Software Center? From the libraries as under 10.04?

(2) I am used to Gnome under 10.04. I would like to continue using it under 12.04. What is the difference between Gnome Shell and the Gnome Desktop Environment?

Thanks for any assistance.

Synaptic is a great tool even if with the software center installed and I recommend it. The gnome-session-fallback is much more like gnome 2 in 10.04.

Shell: https://www.youtube.com/watch?v=uMfg7Jsnmg4

Classic: https://www.youtube.com/watch?v=DIQXKrH46wI

You might find some of my notes here helpful:

http://ubuntuforums.org/showthread.php?t=1966370