You need to be more specific, is there no fax icon? Do you get an error when you select the fax icon, does it try and fail to send?
Assuming there is a fax icon (There would be if you ran the setup and have not hidden it), set the volume on outgoing fax to be audible so you can hear the phone/fax call to make sure you haven't simply dialed the wrong number or forgotten to dial 9 to get an outside line etc.
Machine Status > Tools > Service Settings > Fax Service > Fax Volume > Outgoing Ring Volume.
If you can't tell what to do from that, go into Job Status > Completed Jobs and select the fax to see why it failed and report your finding back here.