"Locked Files" shows documents you are currently in the process of editing. It shows you the type of documents you have locked, their titles and which workspace they sit in.
These files are locked to the other workspace members until you have uploaded a new version or unlocked the file within the workspace.
You can click on the file title to be taken to the file details page where you will be able to unlock it should you want to.
This area sits on the right hand side of your dashboard, underneath the "My Tasks" area and the "Files Awaiting Approval" section.