To prepare to start creating programs that use the AdWords API, you should:
Understand what kind of AdWords client the AdWords API is intended to benefit (large customers or those who manage many accounts).
Have a look at the AdWords API home page and documentation center.
Understand the purpose of a WSDL file and at least scan some of the AdWords API services WSDL files.
Choose a development language and SOAP toolkit.
Understand the purpose of the eight different AdWords API services.
Obtain a developer token and a My Client Center logon (if you don't already have one).