Tabs let you quickly connect users with important documents in Office or third-party apps.
To add a tab to a channel, Select “+” at the top of the channel, select a tab and follow the steps. The tab will appear at the top of the channel.
To turn an office file into a tab, you’ll need to upload it to the team's Files tab or attach it to a chat message so it happens automatically. Once you pick your app, it’ll give you an array of files to choose from.