Purpose of GIMP
Gimp is a Graphic Image Manipulation program (similar in nature to Photoshop)... The main use of GIMP is for image retouching and editing...
The GIMP application has the following features:
Coloring Selection and Paths Image Editing Layers, Layer Masks, and Channels Automations, Scripts and Plugins Generic Graphics Library (GEGL) Multiple File Formats
Documentation
Gimp Manual: http://docs.gimp.org/2.6/en/ (See "'Table of Contents" section)
Online Tutorials
Gimp Tutorials: http://www.gimp.org/tutorials/
Textbooks
Publication List: