There are many excellent books on quantum theory from which one can learn to
compute energy levels, transition rates, cross sections, etc. The theoretical rules
given in these books are routinely used by physicists to compute observable
quantities. Their predictions can then be compared with experimental data.
There is no fundamental disagreement among physicists on how to use the
theory for these practical purposes. However, there are profound differences in
their opinions on the ontological meaning of quantum theory.