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
If you look at the snippet page, you’ll see that the &onevote parameter seems to be a boolean : i.e can only be either set to true or false &onevote=`1` or &onevote=`true` I guess. When the parameter is set to true, it seems the snippet uses cookies to remember the vote (thus, not allow multiple votes).
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