I just saw it and as a quick summary for those who didn't saw it yet: It is about a crocodile Makuu who took, by force, a so called "Mashindano", a duel between the leader of the crocodiles (Pua) and its challenger, over the leadership of the group of crocodiles. Makuu didn't want to listen to anyone, especially not to the Circle of Life and the natural order of things and forced the Hippos out of the "Big Spring", a giant lake in the Pride Lands. In consequence, all the other animals shifted their habitats and there is a complete mess now in the Pride Lands. But Kion doesn't want to use the roar of the elders to defeat Makuu and send the crocodiles back. In the end he uses the roar as demonstration of his power that convinced Makuu to leaf the lake. There was a lot of little other stories, including a questionable song, but this sums it up quickly.