New user: How to turn on microphone and camera?

I tried my first jitsi video call yesterday using firefox. I could see the other party, but not hear him and he could neither see nor hear me. Jitsi showed the camera and microphone were not active but provides no way for me to activate it, based on my looking at settings and other icons on the screen.

How to I get jitsi to recognize my Logitech C925e webcam and microphone, or the microphone on my Yamaha CM500 headset?