You can change the date & time format in Google Sheets & Excel Online using this guide. Use different date & time formats in spreadsheets.

You can easily hide and unhide columns in Excel by individually revealing hidden columns or using the "Format" option to unhide all hidden cells.

If Excel Online is not working and you see errors Couldn't Open the Workbook, or Request Was Taking Too Long, then see this post for the fix.

Formulaic conditional formatting rules in Microsoft Excel can be tricky, so learn how to avoid a common mistake.