Brains, plug ins and script are all ways to enhance or expand mach3 to run on more complex machines. If you are new to cnc you likely do not need to use any of these, at least for a while.
To generate gcode to run mach3 to make a part can be done with wizards or CAM software. Some common CAM software is sheetcam, cambam, cut2d or other vectric products.