請問為甚麼很多英文指導書都是什麼101？

101 means the basic course. This system is used by USA.
In the University, they always use 101 for the entry course.

in the US when u go to college all the course u take are all basic things. They are all assigned a number usually is English 101 or History 101. When u get to the second year the class will be English 201 or 220

In US college system, classes are categorized into different codes in terms of their difficulty. The easiest series is 100, then 200, then 300 or even 400. The code 101 means the first cource in the easiest category, which usually means introductory class.

______ 101 then means the introduction to that particular subject.