Can my boss give me a shift that conflicts with my church attendance, if I asked him or Sunday mornings off before he made the schedule?

Businesses must make "reasonable" accomodations for employee religious observances. If Sunday is the time for your worship services, then--assuming that there are other shifts you can reasonably do (e.g. it's not that Sunday is one of the business's prime times, and you can't do the job you were hired for without working Sunday), then the business should have scheduled you for different shifts.