The Law of Reflection states that the angle of reflection is equal to the angle of incidence.
Typically, diffraction from a reflective grating produces multiple diffraction orders: 0, -1, +1, -2, +2, and so on. The 0th order is the ordinary reflection. The other orders are offset from the 0th order according to the grating equation. The detailed shape of the grooves in the grating affects how much light goes into each order. This is explained here.