Knowing how to define the API query parameters to pull out the data from Google Analytics profiles is imperative.
The reference guide from Google unfolds the defining methodology required to retrieve data from GA using API powered scripts.
There are two "super-duper" high level roofs containing thicker and thinner branches which you might want to know while dealing with GA API enabled reports. They are
1) Core Reporting API
2) Multi-Channel Funnels Reporting API
Here is the link to the API reporting developer guide