Check-out a file from the Project Navigator to work exclusively on it in a multi-user environment.
The file is checked out in your name.
Check in the file you are working on to allow others to view it and have access to it.
Once you have completed making your modifications to a drawing you have checked out
The file is checked-in with your comments, you user name, and your domain or computer name. A backup file, with the drawing name appended with check in time, is created for your modification in the same folder as the drawing.