The brown stuff is the limescale from the inside of the iron coming out. It means that you are successful in descaling it. I would repeat the process until no more brown gunk comes out.
Then once all the steam is clear, you can clean the soleplate by wiping a lemon/vinegar soaked cloth over the hot iron. I personally would keep wiping while the brown gunk is being spat out, as it will stop it drying on the plate an d becoming a more ardous task.
Nb, when you use the iron after decaling ie if it cools down and then reheats you may get some more gunk. Lots of swishing the descaling solution around, and giving the iron a few good blasts of steam on that first reheat (onto an old rag) before ironing any clothes should prevent clothes being gunked.