Hello there Woojung,

Thank you for submitting your homework. Please check and take notes of my correction Thank you.

Corrections:

I usally get 3-5 homeworks everyday.

Correct: I usually get 3-5 homework everyday.

** Be careful with the spelling of "usually".

** The word "homework" doesn't have any plural form, So we should write it like that.

To me I think homework is fun and best to do in studying.

Correct: For me doing homework is fun and best to do in studying.

** Be careful with your sentence construction.

** The word "to" and the phrase "I think" is not appropriate for your sentence. Use "for" to mean that you are sharing or giving your opinion.

I think good thing for doing homework is important to students because it helps them study more, make their brains work more faster or helps to grow their brain, and review what they learned in the lesson.

Correct: I think, giving homework to students are essential because it helps them to study lessons that they have learned and analyze them.

**Use the word "essential" to describe something that is very important and necessary.
** Use the word "analyze" to mean "to look at and think about something carefully, in order to understand."

But sometimes homework could be unnecessary when teachers give us a homework that have no relation with a lesson we have in school.

Correct: But sometimes, homework could be unnecessary specially when it is not related to the lessons.

** Use the word "specially" to mean for one purpose.
** Use the word "related" to mean connected instead of  "relation".