$resource, what’s the difference between get and query?

The main difference lies in query having isArray: true :

'get'  :  {method:'GET'},
'query':  {method:'GET', isArray:true}

This means you would use get when requesting a single object, and query when requesting a collection. For example:

Users.get({userId:123}); // returns a single user
Users.query(); // returns a collection of all users.