You can add multiple files to VSS by following the steps below or by using drag and drop. See Add Files and Folders Using Drag and Drop.
To add multiple files to VSS:
Note To select all displayed files, press the HOME key to move to the beginning of the list, then SHIFT+END to move to the end. This dialog box will only accommodate 256 characters.
Files already in the current project are not displayed in the File name list.