of topic: C programming style

[Martin Czech]

What is the usuall C programming style with regard to 
headers and includes?

I guess .h contains no actuall code?

I understand that something.h should contain some switches,
defines and function prototypes with some comments
of all functions in something.c, which contains all the sources.

Is this so?
What is the proper path for  such inlcudes?
Why do I need only to include math.h
for all mathematicall functions, I mean there is no function
code in it. 

How does the compiler know where to get the code for some
something.h header file? 

m.c.