This feature lets you add a reaction to a message.
How it works:
Go to the message you want to react on, and select the emoji you want to react with.
Choose an emoji of your choice-
How the reaction appears once you have reacted-
Purpose:
Adding reactions serves the purpose of acknowledging messages through emojis. It basically helps you to respond to a message with the use of emojis.
Benefit:
Now, instead of typing your message as a reply, you can acknowledge messages using reactions. You can also express your thoughts on the message by adding these reactions.