Noises are organic, chaotic looking procedural graphics. The outputs generated by noises look very different from the artificial-looking shapes of the Patterns category.
You would use noises as a starting point or detail layer for things like grit, dirt, random growth, for any kind of subtle-variation layering, etc...
All noises are fully resolution-independent, so you can scale up or down your result without any fear of ever losing quality.
There are 3 different use groups inside the Noises category. There are the new 3D noises that require at least a baked position map from a mesh, they are intended for very specific use cases. The large majority are the standard noises, that spread a wide spectrum and are useful in many cases. Then there are the Grungemaps, which are compound noises with much more depth and details than standard noises, at the cost of a much slower computation speed.
Some good noises to start with: