You can easily share a file for review and collaboration by your classmates on Chalkup.
Open the discussions creator window by clicking the "Post a Discussion" button in the top right of your screen when in the discussions pane.
(You may also click the small plus button in the bottom left of your sidebar and select "New Discussion.")
When you have a blank discussion open, categorize it as a "Collaboration."
Using the file uploader, you may upload a file from your computer or select a document to share from your Google Drive.
Once the file has finished uploading, add a discussion title and body, then click the "Share" button.
You'll be able to view the full document, as well as comments and edits from the rest of the class, in the detailed view of the discussion.