Select the language of the person speaking, and the language of the person who needs the translation:

Click on the 'Microphone' button:

The user will likely need to 'Allow' Google Translate to use the Microphone, click 'Allow'

Click on the Microphone Button again to start recording, when the microphone is listening the user will see a 'Stop' button (Square inside of a circle). Once the user no longer needs to translate by voice, click the stop button. 

As the voice is being translated, the user can read along: