Marking channels as a favorite is a great way to organize your channel sidebar by choosing which public channels, private channels, and direct messages are most important to you.
To mark a channel as a favorite, open the channel:
On desktop: At the top of the page, select on the star icon next to the channel name.
This adds the channel to a Favorites list at the top of the channel sidebar, so it’s easy to access. To remove a channel from the Favorites list, select the star again.
On mobile: Select the channel name at the top of the center pane to access the drop-down menu, then select Favorite. To remove a channel from the Favorites list, select Favorite again.