Buddyfight ridelines

I wanted to give the Buddyfight decks a try, but I've never played Buddyfight before. So I tried looking up deck recipes to get an understanding of how they are built.

Why do most of the deck recipes involve five cards? I see the standard four cards in a ride line but then they have a creature as well listed as a fifth card and I can't figure out how it's played?

Can someone help explain the basics of Buddyfight decks to me?