Voice Messaging allows you to instantly communicate with a contact or Group Chat. It provides an enriching chat experience, and you can count on it to deliver important and time-sensitive messages. As such, all Voice Messages are downloaded automatically.
To use Voice Messaging, simply tap and hold on the microphone icon next to the text entry box.
While recording with Voice Messaging, you can slide right to cancel instantly.
A really cool and innovative feature of Voice Messaging is that when your Voice Message has been played on the recipient's phone, the microphone icon will turn blue.
After you receive a Voice Message, tap the 
play button to listen.
Hold the phone up to your ear to have the message play through your phone's speakers or simply hold the phone away from your head to listen to the message on speakerphone.
The microphone next to the messages that you have not listened to will be green:
The microphone next to the messages that you have listened to will be blue:
Learn how to use Voice Messaging on: Android | iPhone | Nokia S40 | BlackBerry | Nokia S60 | BlackBerry 10
Cheers,
WhatsApp Support Team