The most convenient and all-encompassing reference tool is The Edge's On-Line Help System, which is built right into The Edge interface and available on-line. From there, you can browse a topic, search the index, or do a full key-word search.
When working in The Edge, many screens contain a yellow Help button built right in; it will automatically open to the topic for that screen. Alternatively, you can use F1 on your keyboard to access the Help menu throughout Edge.