arranging pages as a book or magazine

[zerokilled]

greeting people

i'm not an advanced layout designer but neigther a novice. there is this doubt that i always had, and even been in college i asked the same question without the proper response, or maybe i don't understood. let say you're composing a book of 20 pages. but the book will be printed two pages per spread, back and front. my question is, how the content should flow in the desktop publisher? who is in charge of the page arrangement, the designer or the press?

i'm almost sure that the content flow in sequential. is not practical to scroll page by page to position content manually. this is the way i had been doing for basic design pamplet of 2 or 3 spread, to print in my home. i know in the industry this isn't the best practice. again, when i export the document in pdf, how i arrange the page in the proper spread? if the press is in charge of this task, how they determine this process of page arrangement?

pd: i use indesign cs and above.

thanks for any help