Please try out the new interactive keys to Common Macrolichens of the Pacific Northwest by Sunia Yang and me. These will probably be most useful for someone between absolute beginner and advanced, but hopefully there is something for everyone. Beginners should spend some quality time with the Characteristics page, which contains an illustrated glossary and an explanation of the variables used in the interactive key.
Some parts of this are still in development and we are always trying to improve the underlying data, so feedback on what works and what doesn't work are welcome, as well as any other suggestions for improvement. Please see the "feedback" link on the main page.