When you first start the program, you will see a file tab across the top of the drawing area. With just a single drawing open, you see just one file tab, which corresponds to that drawing. But as you open additional drawings, you will see additional file tabs, one for each open drawing.
File tabs are just one of the new features included in my new iBook, AutoCAD 2014 New Features and Enhancements – Revealed!, published by 4D Technologies/CADLearning. I've uploaded the entire lesson video on File Tabs to YouTube so that you can see for yourself how File Tabs can make it much easier to work in AutoCAD, particularly if you have multiple drawing files open.