I watched Liu Chuan's guitar self-study March, Zhang Wenzhong's classic folk guitar course and Lu Jiahong's fingered guitar. Which is easier to understand?

Lu Jiahong's textbook is a very good course to practice fingering solo. The other two practice folk songs. If they are easy to understand, they are Liu Chuan. But to be honest, I think the best guitar playing and singing course now is "Between the Fingers of Pan", but this book is best studied under the guidance of the teacher.