Welcome to the SMG documentation. There are several sections you might be interested in:
The SMG Concepts doc - High level concepts and description of how SMG works.
The SMG Configuration Reference - All configuration objects supported by SMG and their properties.
The SMG Monitoring HowTos - Some example-driven documents describing how to monitor various services types using SMG
The History and Evolution of SMG - This document describes the history of SMG and covers a lot of details about how SMG works but also why it works that way.