There are many open source applications that handle graphics creation and manipulation. Some of the notable ones are:
GIMP
GIMP is an acronym for GNU Image Manipulation Program. It is a freely distributed program for such tasks as photo retouching, image composition and image authoring.It has many capabilities. It can be used as a simple paint program, an expert quality photo retouching program, an online batch processing system, a mass production image renderer, an image format converter, etc.
Official website : http://gimp.org/
Tutorials : http://www.gimp.org/tutorials/
Inkscape
Inkscape is an open source drawing tool that uses the World Wide Web Consortium's (W3C) scalable vector graphics format (SVG). Some supported SVG features include basic shapes, paths, text, markers, clones, alpha blending, transforms, gradients, and grouping. It also imports several formats like EPS, PostScript, JPEG, PNG, BMP, and TIFF and exports PNG as well as multiple vector-based formats.
Official website : http://inkscape.org/
Tutorial : http://inkscape.org/doc/basic/tutorial-basic.html
Scribus
Scribus is an open source page layout program with the aim of producing conformant commercial grade output in PDF and Postscript, along with extensive support for graphical PDF form and PDF presentations.
Official website : http://wiki.scribus.net/
Tutorial : http://wiki.scribus.net/index.php/Get_Started_with_Scribus