The indirect object - the noun that receives the direct object itself.
A direct object - the noun that receives the action of the verb.
1) The painter painted the millionaire a landscape.
Verb: painted
Direct object: a landscape
Indirect object: the millionaire (because he receives a landscape, which is direct object)
2) I sent a postcard to my penfriend.
Verb: sent
Direct object: a postcard
Indirect object: my penfriend (because he receives a postcard)
3) The teacher showed the class a thought-provoking exhibit.
Verb: showed
Direct object: a thought-provoking exhibit
Indirect object: the class (they are being showed a thought-provoking exhibit)
4) My great-grandfather left my dad his gold watch.
Verb: left
Direct object: his gold watch
Indirect object: my dad (who receives direct object - gold watch)
5) We told ghost stories to each other.
Verb: told
Direct object: ghost stories
Indirect object: each other (they were told ghost stories - direct object)
6) My cat brought my mum a dead mouse.
Verb: brought
Direct object: a dead mouse
Indirect object: my mum (she receives a dead mouse - direct object)