OneDrive for Business cloud storage is available by default in Teams. To share files from other cloud storage you first must add them to Teams. For instructions, see Add a cloud storage service to Teams.
Add a cloud file to a channel conversation
In Teams on the desktop or web, go to the conversation and select Attach beneath the box where you type a message.
Select your cloud storage service.
Select the file you want to add.
Note: Contact your IT admin if cloud storage options don't appear.
Add a cloud file to a chat
We don't currently support sharing files from cloud storage services like Box or Dropbox in one-on-one or group chats. You can still attach files from your OneDrive for Business account to a chat message, though.