I need help with figuring out how to work the voice chat.  I have a working headset.

I want to know how to chat with people or (if it's possible) chat with your entire squad.  I also want to know if it's just always sending what you say or if it only sends when you hold down a specific button and if so what button?  I really just need a breakdown of how the voice system works and how to use it.  Thanks!

If you don't completely know how to work it just tell me what you know how to do.  And I'll put the bits and peices together.