The Getting Started page steps you through the process of creating a StubHub account, registering an application, and subscribing to the StubHub APIs. If this is your first visit to the Developer Portal, you'll want to start here.
The API Reference describes each of the API calls and provides specifications of the query parameters and the HTTP request and response properties (in JSON). As you're developing your application, the API Reference will be your constant companion.
The Developer Guides take an in-depth look at a variety of development tasks, such as how to create a login session and how to form the command, headers, and body of an API call. Before you start using the StubHub API, you should become familiar with the material in these guides.
Some of the objects, data types, and data dependencies are common to a number of API calls. The Object Definitions section describes these common entities. The API Reference pages point you to these definitions as they're needed - or you can browse the definitions to get a better understanding of the objects that you'll be working with.