Why won't Installous work?!?

I got Installous 4 and it looks nothing like the Installous I've seen from Youtube videos. Even worse I don't know how it works. It keeps telling me that the IPA is invalid. What foes this mean and what do I have to do to make Installous work? Also, I am using an iPod Touch 4th Gen and I jailbroke about 5 days ago.