Hi Ken,
To use a microphone you will need to have the "Mic" control section enabled. This can be found above the left channels volume control in the mixer section. Once the mic widget is enabled you can adjust your mic's volume etc there.
We are not sure 100% that this provides a "talk over" function though which lowers the music's volume, so you will most likely have to do this yourself by lowering the channel faders when you wish to talk. Although, its still worth testing this yourself to see what it can do as we have not tested this out ourselves.
You can also find the "User Manual" in the help manual.
