An upsidedown fire is when you put the big stuff on the bottom and build up, gradually moving through fuel, kindling and then put your tinder bundle on top. (With more kindling - your standard loghouse or teepee fire - above that.) The fire will burn down, so that it's essentially self-feeding. Less work when you're cold and wet is a plus in my books.

Here's a youtube video:

http://m.youtube.com/#/watch?v=ubPYIl9IFdQ
(Equipped to Endure)

Try this one:
http://m.youtube.com/#/watch?v=pjBfzyz-xM8