For context: FreePBX is an open source web configuration UI for Asterisk, which is a powerful VoIP / telephony (SIP) server.
With Asterisk, you can for instance take calls, build menus you navigate by dialing stuff, take passwords from the telephone keys, route calls, etc. Configuring Asterisk can be quite difficult when you do this for the first time, there's a lot to understand and the syntax can feel a bit arcane.