all u have to do is create a new folder name is 'SP Scenarios' and put it in the RON folder on your computer which should normally be here:
C/:programfiles/microsoft games/Rise of nations
then dload the file and save it in this new folder. The file will be a .zip file. So, you have to extract the files in the same folder and then start the game and then select solo game and then load a scenario then navigate to the 'SP Scenarios' folder and select the file you unzipped.