WordPress Functions Reference
WordPress exposes certain functions / methods that can be used by any theme as needed. If you are already familiar with the programming world, you would already know what is meant by API. WordPress has its own API.
These methods cover all the different aspects of a wordpress based website and they expose enough parameters so you can customize their output.
Sadish Bala is a guy from India, working as a software engineer in the USA. He has created many popular WordPress themes. You can learn more about him at 