if they have a soul in them, then get into the arcane university and use an altar of enchanting to put enchantments on your normal weapons, or equip them in the inventory to recharge weapons that already have an enchantment. if they have no souls in them, you can cast a soul trap spell on a creature (only black soul gems can contain humans) and kill the thing you casted the spell on while it's still in effect. if you do that, you will trap the soul in the gem. now go and enchant. oh, and you can enchant armour and clothes, too.
First you have to fill them by killing a creature who you have cast Soul Trap on. This captures their soul in one of your gems. You use the filled gems when making enchanted items, or to recharge items that have had their charges depleted.
You don't 'use' it as such, you just bring it to Hannibal Traven when he sends you to get it, and then it stays in your inventory. You never need to use or activate it during the final mage guild mission, just have it there with you.
It's something that will be used during the last quest for the Mage's Guild. Spoiler - the Archmage will sacrifice himself to put his soul into the gem, and then this will protect you from the magic of Mannimarco (the head Necromancer) so you can kill him.
Basically, Any sentient human being or dremora soul can be placed inside the gems, and will automatically equal to a Grand soul (highest level soul in the game)
No. Soul Gems are used for enchanting and recharging magic items.
Black Soul Gems are the only soul gems that can trap the soul of an NPC, including all ten playable races, and NPC daedra such as Dremora, and Shivering Isles' Aureals and Mazken.
You can use it to enchant an item, or use it to recharge an item that is running low on power.
most alchemy shops will sell them. try the imperial city market district.
It works the same as a black soul gem but it is reusable. The black soul gems ubsorb human souls.
GET soul gem and unlock the soul gems upgrade
there are soul trap spells you can purchase, cast the spell on an enemy and kill them while the spell is still active, but you need to have a soul gem in your inventory to hold the souls you capture. There are also soul trap staffs if you are too sucky to use the spells.
you find sunburns soul gem in his adventure packs level
Darklight krypt is where you find sunburns soul gem
Select the weapon in your inventory, you'll see the usual options to drop or equip at the bottom of the screen, but there should also be a Recharge option. Select this, and you'll be prompted to select the filled soul gem you wish to use to recharge it.