Nice to see you're still going through with the tutorials, if you take a peek under our HTML5 tutorials, you will see a section on counting here: http://devcenter.kinvey.com/html5/guides/datastore#counting and it's mentioned down below again in reductive functions. Essentially the count(query, options) command will count the number of items returned by the query.
about 4 years ago
...where the collection is the set of users. I get it now. Thnask