We describe the world and the way it evolves, the patterns/regularities that we see in it.* We take note of our part in this. We try to do this in as compact a fashion as possible. These descriptions may make use of sentences in a natural language, equations in a system of mathematics, diagrams and icons or what have you.** By a "law of nature" we simply mean a rather good description of some pattern(s) we see in the world, some regularity.
* See my blog of 1 Sept. 2012.
** Maybe we might use a pattern of musical notes. Certainly we use spoken sentences, lecture. (Spoken language may have come a million years before written language.) Musical patterns may be well suited to expressing and conveying things like energy, excitement, and emotions.