most alchemy shops will sell them. try the imperial city market district.
No. Soul Gems are used for enchanting and recharging magic items.
You can use it to enchant an item, or use it to recharge an item that is running low on power.
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)
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.
in the level empire of ice but you have to buy it
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
If you buy Pirate Seas, the soul gem is something with a cannon. I'm not sure where it is, but it is definitely in Pirate Seas. If you go by the cannon on land go right up the stairs and you will find the soul gem.
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.
Whirlwind's soul gem is on Chapter 17, Creepy Citadel. After the little goblin puzzle, there is a platform with two Gargantulas. Defeat them to open the gate and get the soul gem. Hope this helped.