Simply go to senery and then objects and choose away!
Chat with our AI personalities
http://rct3.sourceforge.net/tutorials/beginner_tutorial.html^^ read that tutorial ^^
Use the PgUP and PgDn keyss :)
If you created a Sandbox park, it's in your documents in a folder marked rct3. From there open the folder that says parks. You can't open your park but you can look at the past parks you created.
JCats sets you can dowload it at trackworx.com
http://rollerchamps.weebly.com/dowloads.html