Ehem...Not to be rude (I was once a NOOB myself) but if you are asking the question you just asked, you really need to do some outside research about connection to a Linux device over Ethernet. If you don't have a handle on that and other fundamentals of Linux operation, you will find operation of the BBB to be really frustrating until you have made enough mistakes that operation finally sinks in. And that kind of education is unnecessary.
Do a search and you will find plenty of tutorials, BBB-PBXIAF related, RASPBX related and general Linux related that if you study over time will give you the knowledge needed for empowered operation. I must have over 50 bookmarks of pages that I used to guide me operating the BBB and while I would consider myself a competent operator, there are still lots of aspects of Linux that I don't quite have a mastery of. I am not saying it is easy but once you get it down it's nice having the added knowledge which I have found lends itself to other things I tinker with.
Good luck.