Why is my Nikon D80 shooting so slow?

I click the button to shoot it makes a sound but the picture isn't taken until 6 seconds later until the second sound. What's wrong?

Maybe it is not focusing. Select manual focus then try again. It should take a pic straight away.

In single autofocus mode the camera will not fire until it is in focus.

Sounds like a slow shutter speed. When taking pictures at such slow shutter speeds, the first sound you here is the mirror flipping up to allow your sensor to capture the image, and the second sound occurs at the end of the exposure where the mirror flips back down to allow you to see through the viewfinder again. To fix, use a higher ISO setting, or a wider aperture setting.