Go into the file that you downloaded and double click the RCTN.exe this should put you into the game.
I would recommend getting WinRAR if you don't all ready. https://www.win-rar.com/start.html?&L=0
Once you click this I should take you to the official page.
Do not click the buy button if you don't want to spend money, click the download button underneath. If you are on a 32 bit system click the smaller button underneath that says click here for 32 bit version.
After you have done this it will once again ask you to buy but if you don't want to than once again click the download WinRAR button.
It will than download and show you the steps on the site.
Finally, follow the steps in the first paragraph.
As you use WinRAR it will continue asking you to buy the full version. You don't need it.
Hope this helped!
Another thing you need to do is make sure you are opening the RCTN.exe file in a folder with the RCTN_Data folder in the same folder.