I have found the information on downloading objects (rollercoasters ect) into my game but I have stream and do not have the files in my computer to put the downloads into so how do I download and put into stream online?

Do you mean Steam?

This wasn't the exact place to put this...but welcome anyways! I wish I could help you out, but I am not affiliated with Steam. Do enjoy the site, though!

It depends on the download, but there's a certain place in your computer you have to put them. If you're on a Windows computer, you can go to documents/rct3 and youll see a bunch of folders (Coasters, Structures, Parks, etc) where you can paste the downloads accordingly. For custom scenery, extract to Windows (C/Program Files (x86)/Steam/Steamapps/Common/Roller Coaster Tycoon 3/Style/Themed

What kind of download is it?