How to make sure you have access to in game voice chat. This should work for the majority of players, but as with all things audio related it may not work for everyone.
How to Use Voice Chat
Sound Control Panel
Press the Windows Key and type in Sound and go to Sound Settings.
On the top right you will see Sound Control Panel, click that.
Default Communication Device
This is the important part where some people may not have configured.
Go to both your desired playback device and desired input device and right click them, set them as Default Communication Device. The game will only use the default communication device when it's selected.
This may help those that may have multiple microphones or output devices which can make the game not use the proper devices.