asterisk users - Aug 2004 - newbie question about PBX Call Pickup

Hi,
sorry for annoying question;
i read http://www.voip-info.org/tiki-index.php?page=PBX%20Call%20Pickup
without understanding:
1. how to add an ext. to a pickup group (ie:. how to populate pickup group)
2. how 'Directed pickup' does work?
"You dial the pickup number and your extension, and the call will only 
transfer if it is your extension"
should i digit something like '*8",  then dial my extension?
i tried to dial my extension but i got a busy tone
	maurizio