Ok. so i read the last post where it talks about how to make them, but im still confused.

So first you get a grand soul gem(which i have) empty or filled. Then you put it on an alter at night. So what is this alter that you are supposed to put it on?? is it the alter in the arcane university where you make you spells or enchantments??? or is it some other alter that you are talking about???

Just go through Arcane University storyline.You will come to an altar in front of a necromancer cave.You can make Black Soul Gems there,with the method yoy already know.There are more locations (i'm 100% certain there is a Black Altar near a fort somewhere),but the one you will see in the storyline will do just fine

Ok thanks

Yeah I believe I saw one around a fort near Kvatch-Anvil country. Also near an Ayleid statue holding ruin sort above Blackwood area. And your definately right about the mages guild storyline and cave part. So as long as your in the mages guild, you find about black soul gems eventually.