Files can be uploaded to Team channels and chats.
You can also attach files by:
Watch this tutorial for further review of Sharing Files in Microsoft Teams
Microsoft Teams lets you share and edit documents collaboratively, meaning multiple members of your team, chat, or channel can edit the same document at the same time!
1. From a channel or chat, select the Files tab. Locate the file you’d like to edit, then click the More options menu
2. From the menu that appears, select how you’d like to open the document for editing. Documents can be editing within Teams, Office online, or using the Office applications installed on your computer.
3. Begin making edits to the file. Others who are editing the file with you will appear as colored flags within the document.