Most browsers will ask you for permission to use your microphone when you load up the SYNKii Classroom. 

But if you're having trouble, you can check whether your computer is detecting your microphone in your browser settings:

Settings > Privacy and Security > Site Settings > Permissions > Microphone

Also, make sure that:

• Any external soundcards or interfaces are plugged in and turned on.
• Your microphone is plugged in and turned on (you may need to turn on phantom power if using a condenser microphone).
• Your speakers are turned on, and the volume is turned up. 

If you're having issues with your hardware, you'll have to contact the device manufacturer for support.