The main difference between a direct object and an indirect object is the role they play in the sentence.
1. Direct Object: A direct object receives the action of the verb directly. It answers the question "What?" or "Whom?" after the verb. In the sentence "Tonya mailed her brother a postcard from Australia," the direct object is "a postcard." It directly receives the action of the verb "mailed."
2. Indirect Object: An indirect object, on the other hand, is the recipient of the direct object. It often answers the question "To/For whom?" or "To/For what?" In the sentence "Tonya mailed her brother a postcard from Australia," the indirect object is "her brother." The direct object "a postcard" is sent to the indirect object "her brother."
To summarize, the direct object receives the action directly, while the indirect object is the recipient of the direct object.