open script editor and type in spinFaces with a capital F. hit execute in the command menu , It might give you a error if your using older versions but dont worry about that. at the top of the script editor you will see the word spinFaces;

Highlight that and in one of the drop down menus you will see save script to shelf, hit that it will ask you mel or python,choose mel. Then name the script spinfaces or what ever you like to remember it.

make sure you have put the spinfaces script you downloaded into your script folder beforehand for your version of maya or the instructions I gave you wont work.