If your Excel Sheets are stored on a shared location and you also want to tracked who opened that Excel and Saved it then use the following steps.

1. Create a Sheet named "Log" with the following format.

Timestamp	Username

2. Copy the following code in the Workbook_Open Event

Private Sub Workbook_Open()
Worksheets("Log").Range("A65536").End(xlUp).Offset(1, 0).Value _
    = Format(Now(), "mm-dd-yy HH MM AMPM")
Worksheets("Log").Range("B65536").End(xlUp).Offset(1, 0).Value _
    = Environ("UserName")
End Sub

3. Next whenever anyone opens the Excel Sheet his name will be stored in the Sheet "Log". You can hide this sheet so that others cannot see and modify it.