I feel so dumb. I spent Mirian, or currency basically to unlock my gem slots for my weapons... But now what? I keep accumulating money and I don't see what else I can spend it on! I heard skills can be upgraded? But I can't seem to do it.

@sarnecki: when in the equip menu you can see that you can upgrade epic (legendary?) Weapons if you do the prerequisite task. Usually something like kill a level 40 machine orc or something like that. Mirian, i believe, can also be used to purchase war chests.