The Amount slider is, I think, self explanatory.
Detail attempts to differentiate between noise and image detail. 50 is default; less than 50 and you are blurring more noise and taking more detail with it. Above 50 you retain more detail and increasingly more noise, It's a balancing game to find the right compromise and there is no magic number.
Contrast: NR is essentially bluring and blurring reduces contrat, just as the opposite of NR, sharpening, is essentially increased contrast across edges. With the Contrast slider you can attempt to return contrast lessened by the NR. It's presence there is basically a convenience - you don't need to keep returning to the Basic panel to find the right balance. Of course, too much Contrast (like too much Detail) can counteract the NR.