It can, but it is very bad practice to do so in a normalized database, no
calculated data should be stored unless the work involved in re-creating the
calculation is more cumbersome than current equipment could be expected to
acheive in a reasonable time.
That's correct. You can use a query:
Total:[FieldA] + [FieldB]
or directly in the control source of an UNBOUND control on a form or
in a report:
=[FieldA] + [FieldB]