Hover on a message and click , then select a reaction. After you've added a reaction, it appears below the original message, and if you want to remove your reaction just click on it again.


 

You can add two reactions to any message, and if you hover over a reaction, you can see who added it.

If you're using Webex Teams for mobile, you can see when somebody has added reactions using the desktop app, but you can only tap their reaction to add another instance of that reaction.