Help me configure my Twilio call add-on and my Twilio fax number

I use Twilio and have a call add-on that I have purchased and have a fax number that I want to make sure is properly configured. I am having problems when it comes to the Callback URL. Not sure how to use the callback URL, so I am looking for someone who can properly configure the call add on and make sure the fax is/will properly send and receive faxes. Also, if you are able to configure texts messages so they are sent and received from my email account, that would be useful too.