Vague response to vague question.
Use a UNION ALL query as the source of a Totals (aggregate) query.
or try something like
SELECT Sum(RecordCount) as TotalRecords
FROM (
SELECT Count(*) as RecordCount
FROM TableA
WHERE SomeDate = SomeCriteriaDate
UNION ALL
SELECT Count(*)
FROM TableB
WHERE SomeDate = SomeCriteriaDate
UNION ALL
SELECT Count(*)
FROM TableC
WHERE SomeDate = SomeCriteriaDate)