Sip.conf and extensions.conf

My setup: sip server ->asterisk -> xlite(10 digit phone number)

I tried testing the sample configs sip.conf and extensions.conf but no luck. Can any body help for a brief config of sip.conf and extensions.conf? All I need is to make an outbound and inbound long distance calls(i.e. xlite to pstn or mobile numbers and pstn/mobile numbers to xlite)

fisrt of all read voip-info .org & search for asterisk sip & extension.conf here you get all the paramters that you need to set for each type of calling . then you decide which paramters you need as per your set up& requirement of dailing
to make out going call to long distance

exten => _1xxxxxxxxxxx,1,Dial(SIP/${EXTEN}@host,12)

where host is ur outgoing peer which u mentioed in sip.conf. this is bascally to route call to ur voip service provider. in that peer u plz mentioed domain or ip of ur voip provider gateway
EXTEN Is current dailing extension like 302…
so try it