Assume that you have a list of dates and want to sort it by the most recent one. What you have to do is loop through the items of the list and use the "Convert Text to DateTime" Action, so as to convert  the items to DateTime type variables and insert each one of them into a new list.

At this point, you have converted a list of text variables to a list of DateTime variables.

Then by using the "Sort List" Action, you could sort the dates so as to start from the most recent one.