Do you have IAX or SIP trunks? Your best bet in starting off is just going through the traffic wizard. When it asks you for the IP address of the VoIP device, enter your Asterisk's IP address.
If you have SIP trunks, you need to prioritize UDP ports 10000-20000 (or whatever your RTP stream is set to). You don't necessarily need to prioritize the UDP 5060 for SIP because that's just the signalling port.
If you have IAX trunks, prioritize UDP port 4569.
That should get you started. If you have any specific questions, post back and I'll try to help you.