SAPUI5 is the development platform that is used to create the new bread of SAP Fiori apps. The SAPUI5 tool-kit includes many sections that help you get to grips with the development platform and takes you step by step through the process of using it and creating compatibility Fiori apps.
There are many sections to the tool-kit which including a developers guide, controls examples, demo apps and the explored tab which provides information on components such as buttons, links, menus etc as well as example code used to create them.
Anyway check out the SAPUI5 development tool-kit for more information!!