Welcome to the Guild Nicolas. There are a few programs such as Fractal Terrains 3 and Campaign Cartographer 3 designed specifically for the creation of maps. However most people here use graphics software such as Photoshop, GIMP, Illustrator or Inkscape to create maps. If you are looking for something free, GIMP and Inkscape are just the thing. There are many good tutorials here in the tutorials section on how to create maps with GIMP. You should start by looking at the "Maps in PDF format" sticky in that forum, since the tutorials are organized by software there.