Noise is a good start, but it looks pretty ugly all by itself. We can use noise to make a more interesting function called turbulence. A simple turbulence function can be computed by summing many different frequencies of noise functions:

One Frequency	Two Frequencies	Three Frequencies	Four Frequencies

Now we're getting somewhere. But even turbulence is rarely used all by itself. We can use turbulence to build even more fancy 3D textures...