can someone give me an example of a formula that will look at the
contents of one cell and if that cell is =0 then another cell will
give todays date and time?

Maybe it'll meet your need to put the number in A1 and this formula in the
"other cell":
=IF(A10, NOW(), "")
You can format the other cell as "date and time" using
Format Cells Number Date
And choosing a "Type" you like.

The date and time updates when somebody makes a change in the workbook.