i'll walk you through it...
take it all off, then pull the housing out passed the cable and cut an inch or so off of it with some good cutters, a hacksaw, cutting wheel, whatever you have.
the housing is spiral wound steel covered in plastic, and if you use cutters, it'll leave a bent, sharp end. you can nip at it with the cutters to clean it up, or file it smooth.
then poke a small phillips screwdriver, or a nail or something in the hole and twist it around to make it all pretty.
then push your inner wire back through, and hook it all back up.
if you mess it up, you can buy a replacement brake cable from any bike shop for a few bucks.