Walkthrough: After riding the rail as electricity into Cascade Kingdom, you'll arrive at Waterfall Basin apart of Fossil Falls. Cappy will immediately suggest you start looking for your first Power Moon, the same that will be used to power your very own airship to get to Princess Peach.
Begin your search by claiming your very first checkpoint. From there, find and obtain three Purple Coins by looking through the fossils behind you. After snagging them, head up the path to come to a white hat symbol. By throwing Cappy at it, a platform will be created that will allow you to obtain regular Coins as well as more Purple Coins to the left of the falls. After obtaining all of them, make your way up and to the right. A stream of enemies should appear as you do, but they can easily be defeated by using Cappy. After taking care of them, head onto the ridge near the glowing rock that is guarded by a Chain Chomp.
Before attempting to face off with the Chain Chomp, head over to the cliff on right to find a platform holding even more Coins. Once those are collect, go back to the chained beast. This one will stretch itself backward before charging at Mario - like Chain Chomps usually do - allowing you to quickly dodge before using Cappy to capture and control the Chain Chomp. Once you become Chain Chomp, use can use its moves to charge at and into objects. All of the fossils around you can be destroyed to obtain coins, and the glowing rock can even be demolished this way. Break it to reveal your very first Power Moon, and then quickly claim it as yours.