where do i go to do so. believe it or not ive been a big elder scrolls fan but this one kinda is more difficult for me for some reason. thanks in advance.

Go on the inventory, find the item, and press RB... that ofc is on the XBox 360 controller, it's the equivalent button on the PS3 and... no idea what is on the kb...

T on pc, this gives you an list of al filled gems sorted on soul size and you select the one you need. It work the opposite way from oblivion