Hi everybody. I just joined and has been playing RCT3 for a while now. I need help of how to get coasters, parks, and all the other things you can upload into the a file.

Hi and welcome.
The best place to get all of those things is at the Custom Scenery Depot Website. You can search by the categories you mentioned. Here is a link:
The Complete List of Custom Content:
http://www.customscenerydepot.com/cslist/index.php
The Custom Scenery Depot
http://www.customscenerydepot.com/

If you are looking for things already made to use in your park go to the Download section on this website.
There you will find Parks, Structures and other things made by users on this website.
Most of those files would go into
Documents/RCT3/Structures (put the .dat file in here)
Documents/RCT3/Coasters (put the .dat file in here)
Documents/RCT3/Parks (put the .dat file in here)

I hope that helps and I didn't confuse you.
Have fun.

Basically if you want to put stuff in, go to a folder in the c drive called atari if you got it off steam, and that's where you can put in cs and ctrs and etc, custom scenery goes in the style/themed folder
If you want to know where parks, scenarios and coaster designs are saved, that would be in your "my documents" folder under a folder called "RCT3" its pretty straight forward from there, the folders are labelled appropriately

Basically if you want to put stuff in, go to a folder in the c drive called atari if you got it off steam, and that's where you can put in cs and ctrs and etc, custom scenery goes in the style/themed folder
If you want to know where parks, scenarios and coaster designs are saved, that would be in your "my documents" folder under a folder called "RCT3" its pretty straight forward from there, the folders are labelled appropriately

Thanks

Welcome!!!