If you want to get the Graduate/Easy Spin Stamps you need to finish the surf lesson in catchin waves (Surf Lesson is only for Graduate stamp you can get easy spin stamp in Free Style). So First go to the cove and then to the catchin waves game. Then click surf lesson and complete it to get the Graduate stamp. See the video below to see how it's done. Good Luck!
I hope this video helped you get both of the stamps! Good Luck!