Online Store 2.0 introduces a new JSON template format that lets you add new and existing sections to most pages in your theme, and add and remove sections from any page directly in the Shopify theme editor. This feature lets merchants personalize many more aspects of a store without relying on a developer. It also lets developers build maintainable themes with more modular components. For more information, see Shopify 2.0.
Some core pages such as: Password page, Checkout page, Account page, Order page will not support sections on these pages due to the structure of Shopify.
To create page and add sections to every page you want, see this link.