Here are some quick videos by our founder Roger Arrick to help you get started with modular synthesis.  We also recommend checking out our  Youtube channel where you can find 100+ of these videos
Introduction to Modular Synthesizers Five minutes gets you an overview of what a modular synthesizer is and a basic patch example.

Voltage Control

Voltage control is the most important concept to understand about modular patchable synthesizers. It's simple and powerful.