I had exactly the same problem when I first tried to photograph the moon: all I ever got was an overexposed white circle.
The answer is that the moon is much brighter than you realise. Also, unless you have a very telescopic lens, it's going to be pretty small in your photo. If you use one of the camera's automatic modes, the camera will try to get the "right" exposure for a scene made up of lots of black sky and a tiny bit of moon. The "lots of black sky" wins out, the camera brightens the exposure, and you lose the detail in the moon.
The best way to capture the moon is therefore to use Manual mode. This isn't as difficult as it sounds:
- Switch the mode dial to M.
- Set the ISO setting to something quite low: between 100 and 400 should do it.
- Set your aperture setting to somewhere round f/5.6.
- Set your shutter speed to around 1/100s.
Now try a shot and see how it looks. If it's too bright, try a faster shutter speed until you start to see the detail of the craters. If you've somehow under-exposed it, just do the opposite: try a slower shutter speed, a larger aperture or a higher ISO setting.
The main thing is ignore what the camera is telling you! It'll be flashing away like crazy saying your shot is going to be too dark, but just ignore it. We know the sky will be "too dark", but it's the moon we're after. Fold away your targeting computer, Luke. Use the Force.