Start the conversation before the meeting:
You can prep people for an upcoming meeting through a meeting chat (unless the organizer limited the chat).
Right-click the meeting event in your Teams calendar
Select Chat with participants
Type in your message
Chat in a meeting:
In your meeting controls, a red dot on Show conversation indicates that someone posted a message
To view the message, select show conversation Teams Chat Tab icon
To send a message, compose it in the text box and then select Send
Continue the conversation after the meeting:
After the meeting, you can access the chat conversation in several ways:
Select Chat on the left side of Teams and choose the meeting in the chat list
Note that in the chat list, meeting chats are preceded by the meeting icon and have the same title as the meeting
Select Calendar on the left side of Teams. Right-click the meeting event, then select Chat with participants
Or you can double-click the meeting event and select the Chat tab