TB Spreadsheet

For Cell Highlighting, highlight the range / column you want it applied to, click the "Conditional Formatting" option under the "Home" tab of the ribbon bar.

This will give you a drop down of options, you want the first one "Highlight Cell Rules", click on that you should get a sub menu where you're looking for the second option "Less Than..".

Selecting that should give you a pop up window, in the left hand box you will want to enter TODAY() and the default on the right of "Light Red Fill with Dark Red Text" is probably what you want, but you can adjust that further if you wish.

Clicking OK should apply it and will highlight any data less than today as red.

If you need to review the code applied, click Home > Conditional Formatting > Manage Rules - if nothing comes up try changing "This Selection" to "This Workbook".