How to use the 1.8 setting on the 50mm f/1.8?

I own a nikon d90 and 50mm f/1.8 lens. Whenever I change the setting on my lens to 1.8, something comes up saying FEE. How do I program my camera so I can shoot photos using the 1.8 setting?

FEE tells you that you have not set the lens to its smallest aperture and that you are attempting to use the aperture ring on the camera instead of using the aperture control knob on your camera. You need to lock the lens aperture ring to f/22 (The AF-S 50 mm f/1.8 does not have an aperture ring on the lens)

See page 81 and 82 of your user manual

Fhotoace has it exactly right, I had that issue too when I first bought mine and just to clarify it for you, he's referring to the ring that would be closest to your camera body when the lens is mounted.

Where you have numbers labelled '22 16 11 8 5.6 4 2.8 1.8' there's a little black and orange switch. When the two orange dots are lined up the position is locked so that you can use the lens. You never need to manually change the aperture by rotating that ring when you're using a DSLR. The only thing you have to do is the one time setup at the beginning:
1) Take your 50mm f/1.8 off of the camera and flick the black switch with an orange dot upwards so that the two orange dots aren't lined up anymore.
2) Now rotate that bottom ring until your white dot (just to the left of the orange dots) is above the '22'. This is kind of opposite of what you would think, but now you've set it so that your d90 can use the full range of apertures.
3) Flick the lock switch down again so that the two orange dots are aligned again.
4) Put your lens back on your camera and now you can use the 50mm all the way wide open at 1.8 by using your d90 settings dials like you normally would for other lenses and create some amazing shots.

Hope that helps - happy photo shooting!

Leave the aperture ring of the lens to the largest number. If there's a lock, lock it.

I'm guessing you only have to turn the wheel. It depends on what mode you are though so read the camera's manual on how to change aperture settings under each shooting mode.