How do you get this event macro to work?

[kdanilko]

This is a macro I found online to freeze the first tab in my workbook. I am new to VBA, so please explain in details.

Private Sub Workbook_SheetActivate(ByVal Sh As Object)
    Dim sc As Long ' count of sheets
    Dim NewPos As Long ' index of serlected sheet

    Application.EnableEvents = False
    Application.ScreenUpdating = False

    If ActiveSheet.Index <> 1 Then
        sc = Sheets.Count
        NewPos = ActiveSheet.Index
        For i = 2 To NewPos - 1
            Sheets(2).Move After:=Sheets(sc)
        Next i
        Sheets(1).Activate
        Sheets(2).Activate
    End If

    Application.ScreenUpdating = True
    Application.EnableEvents = True
End Sub