The common core objectives for first grade math are listed here (see link below), and they probably are also listed with the Department of Education website for your state and possibly on your school's website or handbook.
http://www.corestandards.org/Math/Content/1/introduction/The common core does not dictate, so far as I can tell, what grading system is used.
I would also write an email to the teacher asking what the grade means, what it is based on, and so on. If the answer to that email does not help, ask for a conference.
