"Touch," as used in computer world, is a term that means to change the date and time of a file.  You "touch" the file with a date you choose.  You can use a file utility, usually named "touch," which is typically run from the command line (as in DOS or UNIX).  In Windows, you can use Finders Keepers™ to change file dates, times, and attributes in a user-friendly environment of dialogs and easy entries.

Shown below is the dialog from Finders Keepers™ that is used to touch files.*  

touch files--change file dates, times, attributes

*The files to be changed are selected before this date-and-attributes dialog appears.

Note that you can change three different dates for each file.  The "Last-modified Time" is the date and time that you see in the "Contents of..." pane in Windows Explorer.  You can see the other two dates in Windows Explorer by right clicking on a file to get the menu, then choosing "Properties."  Many touch programs do not change the files' creation dates.  But if you want a file's original date to be changed, you must change its creation date.