This video tutorial demonstrates a method of painting multiple textures on to a 3D Mesh, using Blender's Node Editor. It is an advanced technique and requires some prior knowledge of Blender's User Interface.
Sorry about the length of this video. It wouldn't really work if I'd split it into smaller segments - you might miss some critical stage in the work-flow.
Don't get discouraged if it seems baffling at first. It took me a long time to figure this method out. Just play the video through a couple of times and try to follow it.