In the TeamSpeak 3 app, click on ‘settings’, you will be presented with the configuration dialog where you can set your preferred voice mode.
Click on ‘Voice mode’ and choose one of the three options: Voice Activated, Push To Talk and Continuous. If you choose to use Voice Activation, make sure to enable “Echo Cancel” in the configuration dialog as well.
Check this video if you can’t select/assign mouse buttons 3, 4 etc. to the Push to Talk function in TeamSpeak.