The SitePoint PHP blog they've posted the first part of a new series about using the eBay API as a part of a product management application. In part one they start by getting things set up on the eBay trading API and creating the database you'll need for the rest of the series.
In this tutorial series, I’ll walk you through Ebay’s Trading API. The Trading API allows you to build applications that can be used for selling in Ebay. Here are some examples of things you can do with the API: retrieve store information, update store preferences, add products to a specific eBay store, end product listings, update product price and retrieve product information. In this tutorial, we’ll be creating an app that allows users to create a product on eBay through the use of the API.
They start by helping you register an application on the eBay developer site and configure the settings to match your needs. They link to some of the tools you can use during your development and some of the headers/content you'll need to set to make your requests. The tutorial wraps up with the SQL needed to create the database backend for your store's settings, products, listings and some sample data to insert.