Within the delivered 'smartstairspackage.zip' , you'll find a folder 'SmartStairs'.
Just place that 'SmartStairs' folder
at:
'/PATH-TO-YOUR-C4D-INSTALLATION/CINEMA 4D R14/Plugins/'
Please make sure that the 'SmartStairs' folder now resides in the '/Plugins/' directory of your CINEMA 4D installation and contains a file ''SmartStairs.pyp' as well as a 'res' and a 'smartstairspackage' directory.
Note:
If you are using Microsoft Windows, you can also use the 'setup.exe' installation assistant - just point it to your CINEMA 4D installation's directory.
Smart Stairs requires CINEMA 4D R13.058+