Camera and microphone don't work

I’m trying to use camera and microphone in Rocket chat that I installed yesterday with Ubuntu and Snap chat, but they are simply not enabled. I didn’t get any errors. the Camera opens a small box but it doesn’t work. with microphone I’m not able to even press on it.
I’m doing a training so I’m not professional. I used youtube videos and user guid to install it. Please make the ansers as simple as possible.
Thank you all