If you really want to make it synchronous, something like this is what your after:
NSURLRequest * urlRequest = [NSURLRequest requestWithURL:aURL];
NSURLResponse * response = nil;
NSError * error = nil;
NSData * data = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse:&response error:&error];
However synchronous requests are generally not used for this. Its far more common to show some sort of loading to the user so they know whats going on. Network requests can take a long time to return (think crappy 3G signal), Having the user click a button and nothing happen until a netwrok request comes back is a bad idea