Are you trying to create your own Management pack for custom needs? Then, you should read “SCOM MP Authoring Guide” to kick start. This gives you some deep insight into classes, relations,, discovery, discovery targets, discovery relations, discovery scripts(basically helps you create custom discoveries), different types of monitors(event, script, service, health, performance, unit, etc), different types of rules(event, collection), tasks, etc. It also helps you to understand how to perform tasks like groups creation, monitor/rules creations, etc.
You can also down full SCOM 2007 R2 documentation from here
Happy SCOMing.