There is no easy answer to your question as there isn't a one-size-fits-all program. Each department, and each school, offers different programs, opportunities, and environments. You will benefit from spending some time researching colleges and universities; they have web pages describing their programs, the schools, and so forth. You may wish to contact the department chair for additional information on the schools in which you are interested. The AAS maintains a list of programs that offer astronomy-related degrees.