Use of "for" and "by"
It is difficult for me the way I have these two prepositions

Question

Answer

Using the preposition 'by'
Showing nearness, cause, or agent.
Examples: He left his briefcase by the door. He was frightened by the loud noise. The rates are regulated by the central bank.

Using the preposition 'for'
1. Showing how or why something is used, or for whom something is done. 
    Examples: This folder is for recent reports. He was honored for his achievements in molecular biology. I have a present for you.
2. Showing how long something happens: 
    He is going to Russia for five days.
3. Showing direction: 
    This is the train for New York. [Note the implied purpose: for = for going to]

ご自宅で快適に語学を学べるチャンスをお見逃しなく。経験豊富な語学講師陣の中からお選びいただき、今すぐ最初のレッスンにお申し込みください！