Each video conference has a separate chat room in which the participants can chat in parallel to the conference. To get into the chat, click on the speech bubble at the bottom left. A chat window then opens on the left in the picture. 

You can also "send a private message" to individual users. To do this, click on the three dots on the person's video window and then on the corresponding button.

Private chat messages also appear in the chat window, but are marked separately: Messages to all users appear in blue, private messages are displayed in red and under this message it is indicated that only the respective user can read it.

If you do not want to use the chat within the video conference, you can alternatively use the Sdui chat of the corresponding group.