The best way I have found to add information to the Genealogy site is to navigate to a person that is already listed.  From those pages, be sure you have the tab set to "Close Reletives".  This Tab is right under the persons name.

From here you can add Children, Mothers, Fathers, Wifes, Husbands Brothers and Sisters. 

If you need to add an unknown person to make a tree work, you  can use "unknown" as first and last name.  Someone can then hopefully go in and edit that as needed if they know more about that person or family.