Im doing vampire quest .How do I fill it?

Equp a weapon with a Soul Trap enchantment or a Soul Trap spell and kill a human being. Black Soul Gems can only be filled by a human soul. It can be any human, a necromancer, bandit, forsworn, etc. I always just whip out my dagger I have Soul Trap on to finish off a bandit. That way I don't commit a crime by killing an innocent person. They fully fill a Black Soul Gem and they deserve it anyway!

Thanks

Why put the ; between soul and gem in the title?? I'm going to be confused all day long...

How do I equip the weapon and where do I find a soul trap ecchantment in my inventory?

Where do I find the spell "soul; trap"?

You can buy it from http://elderscrolls.wikia.com/wiki/Farengar_Secret-Fire.
There are other places to get it, but he is the easiest to find since he's part of the main story and you have to talk to him early on.
Also it's best to use it on bandits or necromancers. No need to kill a friendly NPC just for a black soul gem.

When I need to fill a black soul gem, I go to a city and murder (bound bow with the soul stealer perk) the most annoying people in town. Unfortunately, I have to always save first in case the person I choose is unkillable.

Today, I went to Whiterun and murdered the zealot preacher guy at the Talos shrine and that annoying drunk.

Characterwise, it's all about my mage's spiral into darkness and madness that began when he murdered his first person to fill the Black Star. Now he has Mehrunes Razor and seems to be slipping faster and faster now.

you need a soul trap spell first, you can buy em from wizards in each town or from general stores usually, once you have the spell, get real close to the enemy you're gonna cast it on, and so you cast it on the enemy then kill em, and if you have a black soul gem in your inventory it will automatically fill it up....regular soul gems do the same thing but will only work on non human things like animals.

I killed off that same guy then nonchalantly stashed his body under the little foot bridge. In daylight. Happiest day and best decision of my in-game life.

I gave the filled dark soul to the guy and he said that he would meet meet at dawn at the marsh.I waited but he never showed up?What now?

Help

I went back to meet him at the marsh.He never showed up.Then later in my quest log it says that I met him?Then it says to talk to him and he will perform the ritual to cure me.When I go there all he talks about is the same conversation as before.Therefore I spent all this time doing this quest and Im still a vampire.

I have no idea how to complete this for you. You can try going to the wiki ( http://elderscrolls.wikia.com/wiki/The_Elder_Scrolls_Wiki ) and searching the quest name. Honestly, I wouldn't hold out much hope. Sounds like the quest is broken which happens all the time in my file.

The NPC that I was referring to was someone else (I believe). He's the obnoxiously loud Talos priest in the plaza area of Whiterun.

I wish you the best of luck.