A direct object is something/someone that is doing the verb in a sentence e.g.
"Martha fried some eggs"
The verb is "fried" and Martha has fried the eggs so therefore she is a direct object.
Whereas an indirect object are nouns that identify for whom a verb is being performed e.g.
"Stan wrote a letter to his aunt"
Here, the aunt is the indirect object because the verb is being performed for her.