I read a lot of what to do , but dont understand, i think ,for an exemple, about 10 sec i kill a enemy, then i do what?

Mark the Soul Gem , or?

I cant understand, i have emty Soul Gem,then go in a Obvilion Gate , kill lots E, but no Soul Gem after it?,

I do something wrong, but what?

You have to cast http://www.uesp.net/wiki/Oblivion:Soul_Trap on an enemy. Soul trap spells all have a certain duration, and if the enemy is killed within that duration, and you have a soul gem large enough to capture their soul, then you will capture their soul. The key ingredient that you are missing is the soul trap spell itself.

To collect souls to fill soulgems,You need an empty soulgem, a way of casting a Soul Trap spell (a spell or an enchanted weapon), Tha ability to kill the creature within the time limit of the Soul Trap spell.
The type of creature determines what kind of soul the creature has, and the size of soul gem you need to have to collect the soul. A Mud Crab has a petty soul and will fill a petty Soul gem, but a Scamp has a lesser soul, so a petty soul gem can not hold the soul.
You can store petty souls in any size soulgem, but a soul gem will only hold one soul.

To collect soul you need three things.
1 NPC Animal, Human and/or Beast race to fight against.
2 Enchanted weapon or spell with a Soul Trap Enchantment. For I, I use a Silver Dagger with a 10 second Soul Trapped duration. All you have to do is to fight against the NPC and stab them with the enchanted weapon and kill them before time runs out.
3 Empty Soul Gems which you get in ruins, dungeons, chest and etc. There are full ones there but cannot full them because they are already full.

As the above poster say there are different types of gems for different types of NPC.

Many thanks, i now understand, and will find a Soul Trap Spell, thats what i needed :biggrin:

I miss having the name of the creature you soul trap on the soul gem. There is no point in having a soul gem collection anymore. All of my characters had soul gem collections in Morrowind. I find myself doing less soul trapping because of this. Anyone out there feel the same?

http://www.tesnexus.com/downloads/file.php?id=11710

I just view them as magical ammo for the Ebony Blade ( mah personal fav'rit ). The trouble with Oblivion is Sigil stones are maybe a bit too powerful on armour if you get the good ones, relegating soul gems to weapon recharge. Doesn't stop me loving the irony of using black soul gems on Necromancers, thoough.