Specific issue

One note: I do not know anything about the English language. Excuse me for the facts, please.
I bought Scrivener 2.5 in French.
In the software, I do the layout that suits me (font, size, page breaks, etc.).
When I compile my text to tansformer .mobi or. epub, my whole layout is completely destroyed (size of characters much larger, no management of page breaks, etc…). Why?

Here’s my guess… I could be wrong.

By default, Scrivener deals primarily with font, size and page break during the compile process. Compile options and final output format determine this, unless overriden by specifying that selected items be compiles “As-is”.

From the Scrivener manual, available within Scrivener, also available for download in PDF format from literatureandlatte.com/support.php#Scrivener

in 15.1 Rich Text Editing Philosophy
Scrivener supports a rich text editing environment, which means that it is loosely “what you see is what you get”. Unlike word processors or desktop layout applications, however, the precise formatting that you use when writing in Scrivener may in fact look nothing at all like the final product. The compiler will be covered in greater detail in a later section (chapter 24), but suffice to say that you can work in one font, say the default Cochin, but publish in an industry standard font like Times New Roman, without having
to change your source text. What this means for you is that certain aspects of your editing can be conveyed through the compiler, like a range of italicised text, while the base font itself can be changed beneath that. Scrivener’s editor can thus be used like a typical word processor, but with the knowledge…" There is more…

in 24.9 Separators…
“ePub and Kindle Since page breaks have no meaning in an e-book, the “Page Break” option will be changed to “Section Break”. This will not only cause the e-reader to switch to a new virtual page (if it chooses to display things in such a way), but will also insert the name of the item with the section break into the automatically generated Table of Contents.”

You should definitely take a look at Chapter 24 Compiling the Draft.

You might also search the forums, via the search field in upper right corner, on “page break” and review discussions it finds. One of those, for example…

You might also try the built in tutorial and also view some of the video tutorials, especially those dealing with compiling" at literatureandlatte.com/videos.php

Hope that helps.

Something worth noting is that with e-book publishing you often have very little control on the overall appearance of the text. The reader can only display fonts it has installed, often chooses line-height, justification, margins and text size for you (based on the reader’s preferences). So you cannot expect a literal transfer.

One thing you mention is page breaks, in Scrivener when you use a page break this actually creates a section break in the e-book, and will start a new internal file within the e-book format.