GIMP is a free and open-source raster graphics editor used for image manipulation tasks like photo retouching and image cropping. It has tools for selecting, painting, transforming, and editing images. GIMP provides layers, brushes, an undo history, and various selection tools to edit images. Common tasks in GIMP include opening an image, creating layers, selecting portions using tools like rectangle select or freehand select, and applying edits like filling, copying, pasting, and rotating selected portions. Filters can also be used for effects like red-eye removal.