Unless the book is fairly old, it will be protected by copyright. There are various ways that a book (or other work) can have lost copyright protection in the US, but for now let us assume that the book is protected. (See "Copyright Term and the Public Domain" for details.)
The copyright owner has several exclusive rights -- things that no one can do without permission. One of these is performing the work, for a book that normally means reading it aloud.
However, one thing that copyright does not protect is learning ideas from a book, and then expressing those ideas in one's own words. Anyone may do that without permission.
For example, I may read a Spanish textbook and then make a YouTube playlist about the subjects in the book.
Yes you may do that, without needing the permission of the copyright owner.
Where should I draw the line? Can I use specific examples from the book (like asking to "fill in the blank: I ___ to a beach. (go, am going)" or something)?
That would require permission, unless it fell under fair use. Fair use is an exception to copyright. It is decided on a case-by-case basis, and there are, intentionally, no clearcut, bright-line rules about what is and is not fair use. It depends on the specific facts of the case. Copying a few short examples such as the one mentioned might well fall under fair use. Copying many would probably not. But it would be better practice to invent one's own examples, demonstrating the same principles or ideas as the examples from the source test.
Or is it only ok to just follow the book's path of learning exactly, but without the same examples?
Following the book's "path of learning" exactly is probably less OK than copying a few examples. The way in which the book organizes its lessons is part of what is protected. A new work should have its own organization, which should not follow the source exactly unless the author has permission from the copyright owner.
