Excel Vlookup With Multiple Workbooks

How to use Excel's VLOOKUP function across multiple workbook files.
NEW LINK TO DOWNLOAD PRACTICE FILES: drive.google.com/drive/folders/0B8SBcQXENLjCNXFpRkJ1aDZvcFE?resourcekey=0-s4DU7mhIFgU4EIJdqn1K_w