You'll get this automatically as the story progresses.
Basically, you get a weapon called Hawke's Key and you have to upgrade it. Every floor level you get to a room with an alter type thing and once you activate it, you fight a demon then have the ability to upgrade it. There are three floor levels, meaning you get three permanent upgrades. You get four choices on each floor level.
The first floor gives the options of:
Electricity Damage
Nature Damage
Fire Damage
Cold Damage
The second floor offers:
Armour Penetration
Mana/Stamina Drain
Health Drain
Attack Speed
And the third floor offers:
Stun Chance
Speed Reduction
Critical Chance
Critical Damage