Your question is definitely ZF2-agnostic. It really boils down to OOP basics.
Have you set up your route for snetworkAction? If so, then the contents of your action, to call that other object method, would simply be:
public function snetworkAction(){
$this->curl_file_get_contents( 'http://someurl.com' );
}
private function curl_file_get_contents( $url ){
...
}
I would strongly recommend getting a grasp on basics before going deep into ZF2. It's really going to be a frustrating experience if you don't have the fundamentals down pat. It's a very unique framework, and while excellent, will cause neophytes to bleed!
Good luck man.