learning gtk - callbacks

[greg wolski <gregwolski sbcglobal net>]

Hi there,
I am trying to learn gtk and I have a hard time to understand signals.
This comes from helloworld in tutorial

g_signal_connect (G_OBJECT (window), "delete_event",
                  G_CALLBACK (delete_event), NULL);
g_signal_connect (G_OBJECT (window), "destroy",
                  G_CALLBACK (destroy), NULL);


Question:
How does gtk know what functions it should call?
I mean for me it basically says: call this or this.
Is it about the arguments that are declared in callback functions?
This is a little bit confusing because no arguments are indicated in those connections.

Thanks for any help,