I learned the rudiments of diagramming sentences when I was in grade school. Or was it junior high?
In any case, diagramming is a valuable tool for writers and editors who want to know not only how, but why, one way of putting thoughts on paper is “correct” English usage and another is not.
I often go to the web pages below to make sense of what’s going on in puzzling sentence constructions. Perhaps you will find them useful too.
Large powerpoint presentation
(the link to this presentation is at the center, and also at the bottom, of the page)
This last page offers a full menu of powerpoint presentations, for diagramming, punctuation, sentence fragments, quizzes, and more.