E.g. you have a contact with first name "John Doe", last name and other fields empty. The App asks you on each word of your contact in wich field to reaissgn this word. In this example case assign "John" to first name, "Doe" to last name. Check the settings, do a "dry run" so your contacts don't get touched (just to check the workflow of the App) and start cleaning your contacts names.