The direct object (accusative case) of the verb is a noun or pronoun that receives the action of the verb or shows the result of the action. It answers the question "What?" or "Whom?".
(1) Her essay won the prize. (What did she win?) (2) She called her mother. (Whom did she call?)
The indirect object (dative case) of the verb is a noun or pronoun that precedes the direct object and usually tells "to whom" or "for whom" (or "to what" or "for what") the action of the verb is done.
(3) Tom mailed Marjorie several postcards. (To whom did he mail several postcards?)