About extension.conf

Hi everyone, I am a trainee now undergoing industry training, currently using Wildcard TDM400P REV I as my digium card, I installed Asterisk 1.4.15 as well. Now when I plug in my telephone line to the telephone port in my PC, I can hear the “doo” sound. My next task is to when I dial the telephone, for example 123, it will show up some functions to me. Any idea where I should begin with?

OK, I think I may have explained my situation too complex. Now I bring up the phone and try to dial, but it has this error message = Dec 14 08:31:42 NOTICE[3671]: pbx.c:1741 pbx_extension_helper: Cannot find extension context ‘from-internal’. What should I do to make this run?