1. First time setup: Escape->System->Voice chat
The Voice chat setup is new. At the bottom, there is a drop down menu that lets you choose between Push to Talk (PTT) and open mic. You can set your PTT key here or in the keybindings page (see below). If you choose open mic (not recommended unless you're leading a group or raid) you should set your sensitivity using the little Test Mic button:
In your Keybindings->Chat page there are 3 new options:
The Mute self key lets you close your microphone so no one can hear you. The "Deafen" key makes it so you can't hear chat, and chat can't hear you.