Page menu explained (mostly for later)
One icon on the Composer toolbar pops up a page menu. The top two items let you change the Current page and the bottom one adds a page.
The current Detailed Tree composer view doesn't need the page menu so much - it will be more useful when the coming Visual Composer is added. So most of the time you can ignore the Page menu.
It's faster to tap the Add Page row at the bottom of the list, if that is visible.
This help page was added in case you are wondering why that weird icon and menu are there.
For historical interest, the first version only let you add pages using the Page menu. The simple Add Page row was a user suggestion to improve usability.