Help with asterisk to use voip

Hello to everybody from argentina i said hello. I download the iso of the linux and the pbx Gui. I have to explain a work and i want to use two computers o 3 i don`t now and make a demostration with voip. But i am very lost of where i need i know that i need a gateway to connect de pbx and make voip. and the some kind of software to make of terminal (cisco ip comunnications maybe)
I don’t want to download skype and show it i need something more real. i choose for this.

Or maybe is something more esay i don’t know thank for your time and for the help

Regards :smiley: