Signal-Flow-Graph Video Course
Signal-flow graphs are theoretically very simple, but if you want to master them, you need to practice. With enough practice, they will become so simple for you that you won't even need any written material later in your work.
Our recommendation for this course is to watch the videos 1 to 8, then solve a few of the exercises in the collection of additional SFG exercises, and later watch 9 to 12.