Upload and share files to work with others in Microsoft Teams.
In a channel, on the right side of a message box, click the + button, then Attach file.
Select how you want to attach it:
Attach recent files from the list.
Attach cloud files: Attach files from a team or channel, or from a OneDrive for Business account.
Upload from this device: Upload files saved on your device.
Select a file > Open.
If you'd like, add a message and @mention someone in your post.
Select Send.
Every channel has a Shared tab. You'll find everything that's been shared there.
Select Upload > Attach cloud files or Upload from this device.
Choose your files.