Its a great feature. Now you have the authority to delete your sent message before sender can see that message.
Its an important feature because sometimes we sent an embarrassing message to any one or in any group chat.
But you and the recipient both should have latest version of whatsapp. If you and your recipient does not have latest version of whatsapp then this feature will not be supported and you will be notify that this feature failed.
Remember that you only have 1 hour to delete your message for everyone.
Lets open any contact whom you want to send your message
Now write your message and click on send icon like this
Now you send your message and you can see that
Now click and hold on your message . Your sent message will be selected. Now click on "delete" icon like this
Now you have 3 options
"Delete for me"
Means this message will be deleted only for you. The person whom you sent this msg can see this message
Means cancel your delete option
"Delete for everyone"
Means this message will be deleted and you and the person whom you send this msg, both cannot see this message.
Now click on "Delete for everyone" option like this
Now you delete your sent message and you can see this "You deleted this message"
Now the person whom you sent this message cannot see that message any longer.