If you're just starting the Challenge list would be completely blank of hints. There are 12 pages for Gold Key/Challenge, you have to finish all the challenge on 1 page to get a gold key. Most of these challenges are done in a resort. They include jumping over/off a cliff, getting from point A to point B in a certain time, getting a certain trick score in a single jump, and even greeting people a certain amount of time. I think the full list of what you need to do is unlock once you get every stamp, not sure if this is correct. Some blue balloon gives you hints on how to get some of these challenges.