To send a voice message, start up a chat conversation with a pal then tap on the "audio" icon.
You will see a "record" button at the bottom of the screen.
Press and hold on the button to start recording.
When you're done, release the button. A popup panel will appear.
To listen to your recording, tap on "preview" button (speaker icon).
When you're satisfied with your recording, tap on "thumbs up" to send it to your pal. If you want to record again, tap on "thumbs down" and repeat the process.