There is no tutorial, It is a learn while doing...
The overall idea is JUST like a real book.
You have a BOOK title > eg. like a book title (is like a container)
Suppose it is a book about animals.. you have cats; insects etc.. (idea)
You make (example) 1 NEW book with title Cats and 1 NEW with title Insects.
Now you have 30 pages created.... 16 about different species of Cats and 14 about Insects
Now maybe you have hairless cats or taill-less cats and insects with wings etc...(idea)
Now create a CHAPTER (setting=books/chapter) UNDER (as subfolder) MAIN BOOK: CATS
-- Hairless (chapter includes the pages)
--Taill-less (chapter includes the pages)
You assign EACH PAGE to one of those chapters...
And so on...
You now can have the BOOKS as links in doprdown Or maybe Chapters etc...
That is basically the idea.. do not overcomplicate it.. (staircase alike)
Do consider the post made by @Jimako.
Alternate : manual way>
Create a sitelink (main top bar) Let us call it BOOKS (url = page.php no ? or id)
Now your BOOK with title Vambutų giminės sambūris is a book with an ID too maybe 5 or 6 etc..
Now when you created the main link (BOOKS) you create a link as CHILD from parent (= BOOKS)..
Title of that would be Vambutų giminės sambūris and your URL !!!!!! = page.php?bk=5 (or similar with id number) See the difference? instead of page.php?ID=XXX now BK=XXXX (bk = books)..
I know it is like a spoiler, (why not tell all) but sometimes try things... the more you do and experiment, the better you get comfortable with it.. (i must admit the bk is not commented much (or at all) afaik, but using the system and observe the 'browser bars popup/unders (urls etc..) always give a clue what is happening and what is being called..
Make backups and experiment.. the more you try, the better it will go..
a) download ALL files from server (by FTP) to a folder on a harddisc drive.
b) go to customerpanel (phpmyadmin etc..) and EXPORT the database as sql file. eventually put that one also in that harddisc folder (so all stays together).
A good method to do this is 1 time a month, so you do not loose to many things if something goes wrong..
Restoring (or moving=identical) a site is the other way around : get an empty webserver upload ALL files, and go to database, CREATE the database (by name but empty) and IMport the backupped sql file into that one..
As long as servers stay the same ( files+dbase) nothing much else to do; when moving elsewhere you need to adjust the sites url (may be done in phpmyadmin core table) and change the config file... That is in short the most common working (easiest) method.