The sidebar gives you all the information you need about the chat you're in and its members. It also provides a place for you to take certain actions on the chat, such as leaving it, turning off notifications or inviting someone new into it.
Every chat has a sidebar. It lives on the right hand side of the message window. If you can't see it, slide it out by clicking on the information button which is to the right of the chat title. In the image below, the sidebar is already visible.
At the top of every sidebar you will see the name of the chat, any description set and its icon. Administrators of the chat are able to edit these by clicking on them. Below that there are four sections.
Members and Bots let you view and manage the contacts in the chat, whilst Media and Docs shows an aggregated grid of all the content shared in the chat to make finding shared documents fast and easy.
Chat Settings contains insights on the chat as a whole. This includes a graph of chat activity and sentiment of the messages sent over time.
In direct chats there is an extra graph which shows the times your contact is normally most active, this is really usefful for working out when they're most likely to respond!
Direct chats don't have a Members or a Bots section, since there can only ever be one other person in a direct chat.