If you want to add a header or footer to all sheets, select every sheet by right-clicking one of the sheet tabs at the bottom of the Excel screen and clicking "Select All Sheets" in the pop-up menu.

When you want to add page numbers to a document header or footer, you can use menu commands. However, if all you need is to do is quickly add a page number to the bottom of your pages, you may ...

Open an Excel Worksheet and click "Insert." Click the "Text" button followed by "Header & Footer." Excel switches to layout view and displays three empty header columns at the top of the worksheet.

In Excel’s custom headers and footers box, the ampersand character (&) is used as a marker to indicate that a special formatting code follows. For example, inserting the characters & [Date]& [Time] ...