direct object and indirect object

I don't know the difference between direct object and indirect object.
For the sentence such as "It lasted five years", I don't know whether five years is a direct object or indirect object or anything else.

Similarly, in the sentence like that "It fell five feet", I would like to know whether five feet is indirect object or not.

I am sorry if my question is a stupid one.

Not all verbs take objects (these are called intransitive verbs), and "last" and "fall" are are intransitive verbs. "Five years" and "five feet" are adverbial modifiers.

<<(these are called intransitive verbs)>> --> (the ones that don't are called intransitive verbs)

Not-dummy, a direct object is something that receives the action of an action verb:

--> I ate my dinner. ("Dinner" is a direct object.)
--> I ate it. ("It" is a direct object pronoun.)

--> I wrote a letter. ("Letter" is a direct object.)

An indirect object tells to whom or for whom an action is done, and it comes before the direct object:

--> I wrote my brother a letter. ("Brother" is an indirect object.)
--> I wrote him a letter. ("Him" is an indirect object pronoun.)

"I wrote a letter to my brother" means the same thing as "I wrote my brother a letter", but in grammatical terminology, brother is no longer an indirect object -- it's the object of the preposition "to".

In the examples you gave, "five years" and "five feet" don't receive the action of the verb, nor do they answer the the questions "to whom" or "for whom". Instead, they modify the verb (how long something lasted, how far something fell).

I hope that helped.

Thank you for your help.
You have explained me that a direct object is something that receives the action of an action verb.
If so, in this sentence
"Victims are students."
Is "students" direct object or not?

I also don't understand clearly about auxiliary.
What are auxiliary verb and noun?