Have you downloaded and read the manual? Also, just browsing through the help page on the website, you'll find your exact question and the answer about Ancestry.com

The program checks the genealogy file (ftw or whatever) you select for missing dates, places, etc. If you hi-lite a line in the "to do" box, the lower box describes what it is you are missing and give suggestions as to where you can find that information. I like being able to see which ancestors are missing source information and given suggestions as to where to look.