The button of the Microphone and its settings (the gear icon)  are placed on the right side of the deck as as indicated in the picture below:

virtual studio - now playing

Click on the button Settings to access the configuration of the Microphone settings. A popup window will appear letting you check and save the changes.

virtual studio settings

You can select the source of the microphone through the settings.  Pick from the drop down menu the microphone source you want to use.

virtual studio - select source

Before going live, you can check the microphone settings and if it fits your needs.  While you make this test, check the Microphone and Deck Volume sliders and adjust them according to which level you want the music to have while the Microphone is opened. One more aspect to check is the silence level.

If you want to have the Microphone open and close automatically once it detects your voice you can do so by setting the Silence Level and Silence Timeout accordingly. The Silence Level is the level of sound above which any sound detected will open the microphone. If set to low level it will open easily when a slight sound is detected. This can also depend on the microphone you are using. Once silence is detected then there will be some time after which the microphone will close. This time is set by the Silence Timeout.

Remember always to save the changes you have made!

When you are ready to speak click on Mic button to open the Microphone and broadcast on air.

Finally, you can select if you want you hear the output stream of the station while making the show and being in the Virtual Studio.
Listen Off: Stop audio playback in virtual studio
Listen Stream Out: Listen to the station's output stream. This is the same stream the listeners are listening to.

virtual studio - listen modes

Check out more on the Virtual Studio here .