In Microsoft Excel I would like to format cells for date as 10-10-2010 instead of 10/10/2010

[wlb729attnet]

I'm doing a family directory. I save each family's info separately. How can I save it all in one file to be shared with eveybody?

[#2]

@wlb729attnet 

1. 10/10/2010 is a bad example - it doesn't tell us whether you want month-day-year or day-month-year. Anyway, you can assign the custom number format mm\-dd\-yyyy or dd\-mm\-yyyy to the cells with the dates. But I would prefer to use an unambiguous date format such as d-mmm-yyyy or yyyy-mm-dd.
2. You can store the info in worksheets in a single workbook. Save that workbook to a cloud service such as OneDrive, Google Drive or Dropbox and share it with your family members.

[#3]

@wlb729attnet 

As a comment. Dates in Excel are actually sequential numbers starting from 1 which is equal to Jan 01, 1900 (if you are on Windows). Applied date format is only shows these date in human friendly form. If you are in US and add date as 07/18/2022, your relative in UK who opens the same file, will see the date as 18/07/2022.

Thus don't care about formatting, use your default one.  However, if you enter the date as the text, e.g. 07-18-2022, people in other regions will see it as the same text and they need to convert such text into the date in accordance with their regional format.

However, if you enter the date as text which is only looks like date, e.g. "07-18-2022", it'll be no such transformation. To check, by default text is left aligned and date is right aligned in the cell.