One of the reasons why people cannot hear you or you cant hear anything, is probably because Teams has not been configured properly.

If you go onto Teams and go to the Settings,  and click on the 3 dots next to your profile icon on the top right.

From there you should see an option called Settings, there will be a cogwheel icon next to it.

Whilst in the settings you will need to go to Devices. From there you can see two sections Audio and Video.

In those two sections check that the options are correctly set to your headphones, camera and microphone. 

If you believe that the settings are correct, in the audio section there will be an option to make a Test Call.

This will allow you to test your settings to make sure your headset,  camera and microphone are all working. 

It might also be worth just checking to see if your headset, camera and microphone are all plugged in and turned on.