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Optional: In order to see the Purchase Orders folder on you computer without using the SharePoint website, you need to Sync the SharePoint site to your computer. Steps for syncing your computer can be found in the guide linked at the bottom of this page. Syncing your computer will allow you to view the In site library section from within your File Explorer (Windows) and Finder (macOS) windows.
You will be unable to delete these channel-folders. These folders act as repositories for files shared in the team and therefore you must delete the team if you wish to delete this folder.
In Summary
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The Files tab in Microsoft Teams acts as a window into the SharePoint site that is created for the team.
All the files added to a team are actually stored in SharePoint and can be accessed at the SharePoint website. Teams itself does not store any files.
When creating new channels in a team, new folders are created in the SharePoint site to keep files separate from other channels.
Files added to the SharePoint website will appear in Teams as if added to Teams directly.
Folders can be created on the SharePoint website that will not appear in Teams.
Files added to Teams share the benefits of files added directly to SharePoint: recycle bin, version history, etc.
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