Students work on the assignment by either viewing a document, editing a shared document, or editing their individual copy of a document. The students can attach files, links, or images to their work. When finished, they turn in their work.
Before the due date, a student can unsubmit work, make changes, and resubmit it. After the student turns in a file from Google Docs, Sheets, or Slides, only the teacher has edit access and can make any changes.
For instructions on how to do this, see Submit an assignment.