I've seen videos of RCT3 where on the ride they have doors that open while on the ride. like they have in haunted houses in real life. What I would like to know is how is this managed? I've tried googling moving doors, but all I get are obsolete pages or videos for home improvement. Please share with me your knowledge in full detail. 
Thank you

its from a cs set however i dont remember what it was called

Animated Ride Event Doors by weber at sgw

went there found the download, but it says to put it in the style/themed folder. I looked and am unable to locate it. where will that be?

If you're on windows, use the file explorer to copy the files in the folder into C:/Program Files (86)/Atari/Roller Coaster Tycoon 3/Style/Themed.
If you're using steam, it's under C:/Program Files (86)/Steam/Steamapps/Common/Roller Coaster Tycoon 3/Style/Themed.

After doing that, open up the game and it should show up under ride events.