[quote name='Moxio']Both please.
Ubuntu.

[/QUOTE]
Well, alright. I'll try to explain some things pertinent to what you mentioned.
When you call "sudo apt-get install package1 package2 ... packageN", you're doing a few things.
First, you're using sudo, which is short for "
super
user
do." Sudo allows you to run things that alter your system; it essentially lets you run a command with root permissions without having to log in as root.
apt-get is part of APT, which stands for Advanced Packaging Tool (thanks, wikipedia!), and it allows you to retrieve and install packages from the repos listed in /etc/apt/sources.list. apt-get is a command line utitlity, but it can be controlled with frontends like the Synaptic Package Manager. Synaptic does pretty much the same thing as apt-get, but graphically. It's the default package manager for Ubuntu, so that's the GUI way to play with your packages.
I'm not sure what's up with the GIMP. Have you tried removing it (using "sudo apt-get remove gimp'spackagename") and reinstalling it?