All modules must have at least the following:

static int load_module():

	Do what you need to do when you get started.  This function can return
AST_MODULE_LOAD_FAILURE if an action fails and the module is prevented from loading,
AST_MODULE_LOAD_DECLINE if the module can not load because of a non-critical failure
(the configuration file was not found), or AST_MODULE_LOAD_SUCCESS if the module
loaded fine.

static int unload_module():
	
	The module will soon be unloaded.  If any channels are using your
features, you should give them a softhangup in an effort to keep the
program from crashing.  Generally, unload_module is only called when the
usecount is 0 or less, but the user can force unloading at their
discretion, and thus a module should do its best to comply (although in
some cases there may be no way to avoid a crash).  This function should
return 0 on success and non-zero on failure (i.e. it cannot yet be
unloaded).

AST_MODULE_INFO_STANDARD(keystr, desc);

keystr: Applicable license for module. In most cases this is ASTERISK_GPL_KEY.
desc: Description of module.