To loosen the nut, turn it to the RIGHT. It's reverse threaded to keep it from spinning off when you pedal. There should be a cone nut behind the surface nut/plate that should have slots in it that you can turn with a flat-head screwdriver.

The other side has regular threads, so if you want to remove the chainring, you need to turn the cone nut on that side to the left to loosen it.