Go to their official website and check if they have a developer's section. Look for a link to an API documentation or API reference. If they don't have a section specifically for developers, try searching their website for 'API' If the company does not provide an API, you won't be able to locate it.

The Google Docs API lets you create and modify documents in Google Docs. Applications can integrate with the Docs API to create polished documents from both user and system-provided data. The Docs API lets you: Automate processes.

Developers: These are the primary users of API documentation. Developers use it to understand how to make requests to the API, what data to provide, and how to interpret the responses. They rely on documentation to integrate the API into their own applications or services.

Think of API documentation as a reference manual that has all of the information you need to work with the API. It tells the developer/partner/consumer everything that is possible with the API, and how to get started.