Files that you share in a channel are stored in your team’s SharePoint folder. Which can be found in the Files tab at the top of each channel.
Files that you share in a private or group chat are stored in your OneDrive for Business folder and are only shared with the people in that conversation. These will be found in the Files tab at the top of a chat.
In the Files tab, your teacher might add read-only resources to the Class Materials folder. Look here for important documents that can help you with assignments, projects, or just staying up to date on class expectations.