You seem to not understand how executable code is produced from source code. Here is the short version and it is the same for every compiled language:

When a compiler translates source code it produces so-called object code, also called a "relocatible file". Basically this is executable code but without the provisions to use external functions. What are external functions. For instance, when you use the printf()-function in your code it has to come from somewhere. This somewhere is a (standard-)library. More on that later.

Once you have created object files from all of your source code files you want to create the executable itself. This is done by a linker (the precise name is "linkage editor"), which searches the libraries for i.e. the object code for the printf()-function and adds it to the executable so that it can run independently. This is called "static linking". You need to tell the linker which path(es) to search for eligible libraries, this is where i.e. the "-L" switch comes into play.

It is also possible to create the executable so that the code for the printf()-function is not included into the executable. Since many programs use that function they would all have to incorporate it. It would be easier to just put a reference into the executable and this would load the code at runtime from the library. The advantage is that instead of every executable containing a copy of the function you have it only once on your disk. The drawback is that the executable won't run on its own without the library being present. This is called "dynamic linking" and the libaries that allow for this are called "shared libraries" in UNIX and derived systems, "dynamic link libraries" (DLLs) in Windows. You need to tell the executable at runtime where these libraries are to be found. This is what the environment variables LIBPATH, LD_LIBRARY_PATH, etc. are for.

Finally you can create libraries on your own from your object files: this makes sense if you want to use a function in several programs. You use the command ar to manage libraries: you can add, extract or otherwise manipulate object files to/from libraries with it. In Windows (there is no pendant to ar in Windows) a linker is used for this.

At last: how to use libraries. In most languages a "function" (or "procedure") is a black box: you give it some data in a certain format and it dows something with it, then gives back a return value (and has maybe changed the data, this is called a "side effect" and should usually be avoided). How this is done should not be your concern. (This in fact is one of the tenets of structured programming.) In C there are header files telling you (and the compiler) which "interface" every function has. That is: which data it expects and what it gives back. So, to answer your question: you "need" the header filles and the library itself. Of course you need to know what the functions do, so some text documentation is also necessary.

I hope this helps.

bakunin