The word law has many different meanings. 
- A legal statute or a collection of such statutes.
- Examples: Constitutional law, international law, traffic laws...
- In this sense, laws are typically passed by legislative bodies and may be interpreted by judicial bodies (in western-style democracies, anyway); there is also an enforcement mechanism (i.e., police) that may be part of a well-defined executive branch of government. 
- A proscription or commandment (or a collection of same) handed down by a supernatural being; a covenant entered into with such a being.
- Examples: Mosaic law, Sharia law...
- In this case, the purported law giver (legislative), interpreter (judicial), and enforcer (executive) are all the same entity: the supernatural being. In reality, however, these roles are taken on by ordinary human beings, either through a formal ecclesiastical structure or by less well-defined social forces (cultural mores and taboos, peer pressure, etc.). There is typically an associated concept of reward or punishment after death, but often an extensive body of earthly laws are developed as well, ostensibly in harmony with the desires of the supernatural being.
- A well-established description of the behavior of nature.
- Examples: Law of gravitation, laws of heredity...
- So-called "physical laws" arise from careful observation of nature, usually based on the scientific method. Scientists don't usually conceive of any "giver" (legislative) or "enforcer" (executive) of such laws, although some do invest a creator and/or some other kind of god with these roles. "Interpretation" (judicial) of physical laws, in the sense of whether the laws "are any good", rests entirely, in the scientific viewpoint, in their predictive abililty — that is, how well they predict what actually happens under well-defined circumstances.