You use the email address only to find your friend's ID, if you don't have it. You each put the other in your contact list. You need a microphone or headset attached to your sound card. To make a call, open Contacts, and click the telephone icon next to your friend's ID.
It will ring in her/his speakers, and s/he'll then answer you on her/his microphone. No long distance charges, no telephone! To hang up, click the red phone icon, then close the program. If I missed anything, there is a help file in the program.