Steps say to edit /etc/fstab, but no earlier content describes the content of this file

The flippant answer if "type man fstab"

This course is supposed to be built upon previously taking LFS101 (for free at edX) or the equivalent, and /etc/fstab is discussed there, although I took a brief look and it is also kind of scattered some; there is no section called "fstab".

You are right that these are forward references which do not make life easy. mea culpa. My experience from designing many courses ranging from introductory to advanced linux topics, to theoretical nuclear physics at the graduate level, is that there is nothing more boring than an "axiomatic" pedagogical method; that is where you introduce things step by step as you might in a mathematical proof, so that the whole house of cards is built without any forward referencing. For example, in our developer courses that involve writing code, such a treatment would take several days of lecture without meaningful labs, rather then being able to write code on the first day.

It's also a whack-a-mole game where if you move something earlier to avoid this, it probably discusses something else which is now not previously discussed and the loop goes on forever.

But I think the main thing here is that hopefully people taking this course have already had some experience with Linux, LFS101 level or better, and already know that "man" is their friend. They also do not tend to do the class in strict chapter order.