Why is my damage so low?

[MaraD_]

If I remember correctly, your basic auto attack is your normal damage (excluding enemy defense/buffs/weapon delay effecting dmg/etc)
So a Weapon Skill with 100 potency will do the same dmg as an auto attack.
200 potency would do the damage of an auto attack, but times 2.

Think of it as a damage modifier.
(There's some other parts to the equations, but this is the easiest way to explain it)
Just think of it to mean "Deals X% of the dmg of your auto attack". This of course doesnt quite make sense in the case of magic, but its still along a similar train of logic.
100 potency is 100% dmg.
200 potency is 200% dmg. (Which is normal dmg + an additional 100%. or x2 dmg.)
350 potency is 350% dmg. or x3.5 dmg modifier.

so if your damage would be "59" then a potency of 300 would deal 177 dmg.
Again, other factors are involved, but for simplistic sakes of understanding how "potency" works, this helps.