I never used Start Rating, but usually snippet calls need a value assigned to the parameter... I guess you’re still learning MODx there. Check out the doc, it helps getting through the basics
The &docID parameter is optionnal, only if you need to retrieve the star rating from another document. Then you should use it like this &docID=`5` if the document you want to use has the ID : 5 (see in the document tree the number in parentheses).
I’ll let those who actually used the snippet get into more detail.
Hope it helps