Clicking the shiny new information button shows a dedicated sidebar that provides information about the channel and allows teams to pin items and messages to the channel itself for surfacing later on.
Slack also said that it rearranged the top navigation to help you find starred items and recent mentions from team members in a single click.
The idea is to provide more information about who’s online, the channel’s purpose and more in a single place. The new sidebar is available in your Slack client right now after a refresh.
➤ Channel Information: New, Improved and Shinier [Slack Blog]