WHERE I AM PUTTING THE FILES THAT I AM DOWNLOADING HERE?

The best I can help you with is for custom scenery. You need to go to program files/ Atari/ roller coaster tycoon/ style/ themes and drop them in there but first before you do any of that you need to open the file using a program such as winrar save to your desk top then drag the file into there. I'm still tryingto finding out how to drop tracks and other stuff in so I can use them. Hope this is some help to you.

The best I can help you with is for custom scenery. You need to go to program files/ Atari/ roller coaster tycoon/ style/ themes and drop them in there but first before you do any of that you need to open the file using a program such as winrar save to your desk top then drag the file into there. I'm still tryingto finding out how to drop tracks and other stuff in so I can use them. Hope this is some help to you.

BUT I AM not understand WHERE I NEED TO PUT EVERY THING BECAUSE THE COASTERS AND THE WATER SLIDES ARE DIFFRENT IN THE Directory

First, don't use CAPS all the way! This isn't really a nice thing and in the online community this is a "NoNo".

Second, before starting a thread with such a basic question, maybe use the "search" engine here or on google?!

Two seconds spend on google, and a link pops up to an older RCTgo thread where "Blu" gives a answer about installing RCT3 custom stuff.

Check it out, boy:
where i put downloads in

So long, Cobra