Open a new query
--Add both tables to the query
--Drag from the field in table tableA to the field in TableB that determines
a match
--Double click on the Join line and select option 2(All in Table A and Match
in TableB)
--Repeat if there is more than one field that determines the records match
-- add the fields from table A that you want to see
-- Add the matching field from table b
-- set its criteria to IS NULL

Run the query.

SQL statement would look like
SELECT TableA.*
FROM TableA LEFT JOIN TableB
ON TableA.PrimaryField = TableB.PrimaryField
WHERE TableB.PrimaryField is Null

OR use the UNMATCHED query wizard.
New Query
Find Unmatched Query Wizard