https://openrct2.org/downloads/demo is for the game
https://openrct2.org/downloads/releases/latest#windows for the mod

download the game, put it somewhere. install openrct2 and point it at your RCT2 directory. go to the settings and change the window scale if you want the game to look better. then, click the third button for servers. scroll down and find "wayneradiotv", the password is "ProbablyPostman"