2.  Starting GIMP the first time

The first time you run GIMP, it goes through a series of steps to set up options and directories. This process creates a subdirectory of your home directory called .gimp-2.4. All of the information about the choices you make here goes into that directory. If you later remove that directory, or rename it as something like .gimp-2.4.bak, then the next time you start GIMP, it will go through the whole setup sequence again, creating a new .gimp-2.4 directory. You can exploit this if you want to explore the effect of different choices without destroying your existing installation, or if you have screwed things up so badly that your existing installation needs to be nuked.

2.1.  Finally . . .

Just a couple of suggestions before you start, though: First, when you run GIMP, by default it shows a "tip" each time it starts up. These tips tell you things that are very useful but not easy to learn by experimenting, so they are worth paying attention to. If you find it too distracting to look at them each time you start, you can disable them; but please go through them when you have the chance: for your convenience, you can read them at any time using the menu command HelpTips. Second, if at some point you are trying to do something, and GIMP seems to have suddenly stopped functioning, the section Getting Unstuck may help you out. Happy Gimping!