Google Docs API are invoked using an HTTP request, or can also by using a method invocation in a language-specific client library. These are broadly equivalent, but it’s usually much simple and easier to use the client library.
For these requests, the API returns an HTTP response, which generally includes the result of the request invocation. API Requests can also be done using Client Library. When using this client library to make requests, the responses are returned in a language-specific way. The Google API client libraries provide better language integration, improved security and support for making calls that require user authorization. The client libraries are mostly available in a number of programming languages by using them you can avoid the need to manually set up HTTP requests and generate the responses.