How do readers know which pages wouldn't be there on an online but paper format site?

For example where are Section A pages 2 and 3, 6, 8 etc. How does the reader determine what pages to not bother to look for?

http://www.nytimes.com/pages/todayspaper/index.html
It goes from the front page to
“International”
“Risking 60 Lashes, Iranian Runs for Office So He Can Walk a Dog section A – page 4”