The only types of Linuxes are Debian and Red Hat.
Red Hat uses RPM (Red-Hat Packet Manager), Debian is APT-GET.
Red Hat spin offs...
Fedora, Mandriva, SuSE and so on.
Debian spin offs...
Slackware, Ubuntu/Kubuntu and so on.
If you are good enough you can fiddle with the packets and use one and fit it on other. But as my expertise goes, is way to hard.
Linux uses what people calls now an App Store for more than 10 years. Is called repository. They are several around the world tailored for each distro.
On the Mandriva world is called URPMI (pick and choose the repositories or let the system decide for you) and most Debian based use Synaptic. The same way the Android OS does.
Some Linux distros are really for the hardcore user without any restrictions and freedom to mess with it with absolute control. Those are the hardest one to use and configure like Gentoo. Some are tailored for just the user that just want to use Linux like you would with your smart phone.
So depending what type of user you are you pick the distro that you like.
Linux is not the Desktop Environment, is just a Kernel.
GNOME and KDE are the most popular ones, others are Enlightenment, Ice, LXDE, Moblin, etc... Each distro uses one as a default, Mandriva is KDE, Red Hat is GNOME as an example. Some distro like Mandriva install both or more and you can pick and choose on one install which Environment you want to use at logon.
I hope this helps.
Hi there.I'm just starting with Linux and learn with unixacademy DVDs. The traning comes bundled with bunch of Linux installations. I tried few and when installed can't see much diference between them. Fedora, Ubuntu, Debian and openSUSE are very easy to install. It takes only few clicks. However after the installation is completed, beside thier "welcome" screens I can't find much difference. They all look the same to me. I'm sure there's must be a difference deep down. Can someone tell, if programs from one Linux are compartible with another? Can I take a program from. let say, Ubuntu and run it in Fedora?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic