When a learner clicks on a document link in an evidence card, that document is then copied to their Google Drive for them to work on. The evidence card then shows a submit button which when clicked, transfers the document to the teacher and changes the student permissions to comment-only.
If an evidence card contains a link, then clicking on that link will mark the card as having been started by the learner and they will see a submit button, which they can click to indicate they have completed the task.
Learners can also add evidence cards themselves and attach and submit evidence on these cards.
If a teacher creates an evidence card and does not add any attached documents or links, then learners will be able to attach evidence to that card and submit it.
Evidence card with an attachment:
Evidence card with no attachment: