How do I do this? I am so CONFUSED!!?

I don't understand how to download custom scenery onto Roller Coaster Tycoon 3 Platinum. I've tried many YouTube methods and NONE have worked. Does anyone have a clue on how to download this scenery? It would be GREATLY appreciated! Thank You! And if you own RCT 3, be sure to go to YouTube and enter my contest. Just search RCT 3 Contest and go to Sort By, and Date Added. I should be on that page. my sn is RavBoy5 if u need help!