This feature lets you pin messages in a conversation.
How it works:
Under any channel or DM, hover on the message you want to pin. An action menu will appear. Click on the vertical three-dot icon at the right. Select Pin.
After pinning, the message will be highlighted in the chat showing the name of the user who pinned it above the message.
All the pinned messages will be accessible from two places-
a. on the DM/channel header below the name with a pin icon-
b. from the details of the DM/channel. Click on the info icon on the right side of the header.
Click on the Pinned section. The messages will be shown along the name of their sender name and profile picture, the time they were sent, and the name of the person who pinned them.
When clicked on any pinned message, a modal will be opened showing that message and some conversation before and after it of the respective DM/channel.
You can also perform actions like reply, react, open as channel, share or pin/unpin it from this modal on the messages shown.
This feature serves the purpose of pinning important messages in a conversation, from where they can be easily accessed.
Pinning texts in the conversation highlights them in order to make them easily accessible for you. You can pin all those important messages from different people in different channels.
Refer this video to see more in details - https://youtu.be/IFvDYUd04DY