Within Teamwork Chat you can quickly send one of five reactions to any message sent in a conversation or channel.
To react to a message, simply hover over it, and choose the first option to the right of the message. A drop down with the five available reactions will then appear.
Once you have chosen this the reaction will then appear to the bottom left of the message.
If someone else has already reacted you can click on their reaction to choose the same or just to the right of an existing reaction you can choose a new one.
If a message is sent and it receives a lot of reactions you can see all the users who have sent one by hovering over the reaction and choosing more.
For more information, see: Using emojis in messages