สวัสดีค่ะ ตอนนี้กำลังเรียนแกรมม่าร์อยู่ แต่ไม่ค่อยเข้าใจเนื้อหาตรงส่วนนี้เท่าไรค่ะ
It is true that this difference is not universally recognized. However, let those who make assertions such as "People in the USA never use 'shall'" peruse a good US English dictionary, or many US legal documents which often contain phrases such as:
Each party shall give one month's notice in writing in the event of termination.
Note that exactly the same rule applies in the case of should and would. It is perfectly normal, and somewhat more elegant, to write, for example:
I should be grateful if
you would kindly send me your latest catalogue.
รบกวนช่วยแปลเนื้อหาตรงนี้ให้หน่อยนะคะ ขอบคุณมากค่ะ 
รบกวนช่วยแปลภาษาอังกฤษหน่อยค่ะ
It is true that this difference is not universally recognized. However, let those who make assertions such as "People in the USA never use 'shall'" peruse a good US English dictionary, or many US legal documents which often contain phrases such as:
Each party shall give one month's notice in writing in the event of termination.
Note that exactly the same rule applies in the case of should and would. It is perfectly normal, and somewhat more elegant, to write, for example:
I should be grateful if you would kindly send me your latest catalogue.
รบกวนช่วยแปลเนื้อหาตรงนี้ให้หน่อยนะคะ ขอบคุณมากค่ะ