what does "is filled" mean?

As a conditional option, that is. So if I have a dropdown box where an item is selected? Does that mean the field is "filled" and it will jump to the next page?...that's what I want tp do...I have 4 dropdown boxes--I want people to only pick one item, and when they do, I want do not want them selecting another dropdown box and select one of those option. So, they have 4 potential with dropboxes, each with multiple options. I only want to allow them to select one dropdown box and one of the items within that dropdown box and then proceed to page 2. I tried to use the logic "is filled," but it does not seem to work. Any ideas?

You have the right idea about how "Is Filled" works.  It pertains to the field as a whole, rather than a specific selection. 

For example, if you have 4 drop down fields and you only want them to select something from one of them, you could set up 4 conditions.

If Drop down 1 IS FILLED HIDE Drop Down 2,3,4
If Drop down 2 IS FILLED HIDE Drop Down 1,3,4
If Drop down 3 IS FILLED HIDE Drop Down 1,2,4
If Drop down 4 IS FILLED HIDE Drop Down 1,2,3

If users wanted to make a selection in a different drop down after they made their initial selection, they would need to clear their current selection in order to show the other drop downs again.