A software development kit contains development tools which help all developers to build some good applications for some platforms. Once you design an Operating System, the next process is the SDK. You can build up one software development kit for other developers based on that operating system. An SDK contains a lot about that operating system, which includes the set of header files, libraries, operating system design extensions, other help documentations, runtime and connectivity files.
The SDK will help the developers for creating and debugging some applications during run time of operating system. For SDK of some operating systems, you can have the Platform builder which helps you during the installation of other platforms. The platform builder also follows the important modules in that operating system of designed process. It also helps a lot in the process of SDK because it contains the headers & libraries of all modules and components of specific operating system design.  
There are so many things about the development process of SDK and the programmers should have good knowledge about this while doing SDK programming for some platforms. Incase of some mistake done by SDK programmers while preparing the tool kit then the software will not support your operating system. During the accessing process, it will show some error message. Software development tool kit can be used for crating, debugging and running without errors of any applications. SDK programming is not an easy task for programmers and so the programmer should have good awareness about that software and also about operating systems.