If you can cut of the green nodules and they still have firm non discolored bases, one can sprinkle with cinnamon ( a natural fungicide) and callus and then let it root NOT watering it in a gravely dirt. Important that each time you cut with the knife that you rub the knife down with alcohol. The rest needs to be tossed. Good luck.

It looks like an Echinopsis that is rotted. Like written above, you need to quickly separate the last of the green offsets before they rot too. The rot travels through the vascular system, so anything connected to a rotted brown area will also rot. Make sure the pot has drainage, it is very very difficult to grow succulents without good drainage.