Obviously you can use the weapon you find or purchase, but enchanting your own will typically yield better results. If you would rather use the Soul Trap weapon enchant, then first you must find a weapon with the Soul Trap enchant on it in order to disenchant. You can not have more than one active Soul Trap at a time.
Once Soul Trap is placed onto an enemy, it lasts for 60 seconds.
If you’re going to use the Soul Trap spell method, then you just need to purchase the spell book from a magic vendor. Personally, I think having weapons with the Soul Trap enchant is the best way to go. You can either cast the spell yourself, or enchant a weapon with the Soul Trap enchant. In order to fill a soul gem, you need to use a form of the Soul Trap spell. In The Elder Scrolls V: Skyrim for the PC, PS3, and Xbox 360, Black soul gems are needed in order to trap the souls of humanoids that can’t go into regular soul gems.
