you should go to the dropdown menus in Excel and
choose the one called 'Format', then under that choose the 'Sheet'
option, then under that choose 'Hide'. Shorthand:
Format|Sheet|Hide

In vba:
ThisWorkbook.Sheets("Sheet2").Visible = False
or
ThisWorkbook.Sheets("Sheet2").Visible = xlSheetHidden
or
ThisWorkbook.Sheets("Sheet2").Visible = 0

To make it so that the user  cannot use the Format|Sheet|Unhide... to
unhide the sheet  you can make the sheet 'very hidden':
ThisWorkbook.Sheets("Sheet2").Visible = xlSheetVeryHidden
or
ThisWorkbook.Sheets("Sheet2").Visible = 2

but you'd have to use vba to make it visible again (see below), or be
in the vbe (where you edit macros) to change the Visible property of
the sheet to TRUE/xlSheetVisible/-1 again in the Properties pane.

To make it visible again:
ThisWorkbook.Sheets("Sheet2").Visible = xlSheetVisible
or:
ThisWorkbook.Sheets("Sheet2").Visible = True
or:
ThisWorkbook.Sheets("Sheet2").Visible = -1