If you just purchased a new MacBook Air, then the operating system is OS X 10.11.4. The iOS operating system is what runs on Apple's iPhones/iPads.
There is no manual for Pages v5.6.1. The Help menu : Pages Help : Overview (or Show topics) is the manual. That, and visiting here, using the Pages Support Community search tool, reading posts, or posting a new question yourself.
Of course, if you were to install Office 2016 for Mac, then there is far more Word documentation available, and the power to do real word processing.
If you have chosen a template other than a Blank template, then the template will contain placeholder text fields containing Latin filler that you just type over. Images will be placeholder images, where you replace the template image by dragging/dropping your own image on top of it.
If you have chosen a new Blank template, then you click either Format or Document on the right toolbar, depending on whether you want to format what you have written, or set up your document fundamentals, respectively.