Our computers do everything these days! Watch a movie (or Netflix). Video call someone on Skype. Chat to someone through WhatsApp. Call someone through Facebook.
All of these actions create a burden on the computers hardware, such as the Camera and Microphone. They are asked to do too many things at once and need a break! That's where a restart comes in!
Restarting your computer clears all of these commands from something called the RAM. This means they start afresh ready to handle what ever the hardware needs to do - in this case have an online lesson! Often a restart and clearing temporary settings is all that is needed!