Documentation

GIMP User Manual

GIMP comes with a built-in help system. Once you have started the program, press F1 for context-sensitive help. You may have to install the help pages from a separate package (gimp-help), depending on how your version of GIMP was packaged.

The user manual for the current GIMP release is available in several languages:

English
Croatian (Hrvatski)
Dutch (Nederlands)
French (Français)
German (Deutsch)
Italian (Italiano)
Korean (한국어)
Norwegian
Russian (Pусский)
Spain (Español)
Swedish (Svenska)

Older versions of the manual for GIMP 2.2 are also available in these languages:

Chinese (中文)
Czech (Čeština)

Tutorials

Tutorials on gimp.org

Books

Books about GIMP

GIMP User FAQ

Frequently Asked Questions

Configuration

How to set the tile cache.
The tile cache tells GIMP how much memory it can use before swapping some image data to disk. Setting the size of the tile cache can be critical for the performance of your system.
How to install fonts for use with GIMP
How to use MIDI devices with GIMP