Below are a few links to help you further understand geoprocessing and open-source development:

Geoprocessing topics:

• What is geoprocessing? - an ArcGIS for Desktop Help article that explains how to analyze and manage your data.

GitHub:

• GitHub - GitHub is the web-based Git repository hosting service that Esri uses for source code management, distributed revision control, bug tracking, and other features.
• solutions-geoprocessing-toolbox - The GitHub repository where we keep the Solutions Geoprocessing Toolbox is actually a great resource that explains the tools in depth.