You can check if there is film that has reached it's end by turning the rewind crank. If it turns freely then no film.
The sequence is the A-R selector - ring around the shutter, set to A, shutter is advanced, mirror goes up and you're at the point to fire the shutter. At this point, if you move the selector to R, it will release the shutter but mirror still stays up. Set the ring back to A - mirror is still up, and you can advance the shutter again to get it back in the ready to fire point.