Plagiarism of structure is the use of another's logical order in an essay, steps of reasoning in a paragraph or section, or order of elements in a sentence.
If an author uses six paragraphs to describe in detail the process through which a dictator took power, you cannot construct your essay to copy that exact structure of six paragraphs detailing those steps. You can summarize those six steps within your work, as long as you provide a proper citation.
Additionally, if an author states, "Since the proletariat rose as a whole to support the dictator, they created the means by which he took control," and you change the sentence to say, "Because the great majority, made mostly of workers, got behind the dictator fully, they made the situation in which he came to power," you have paraphrased the author's idea but copied his original structure. Even with a citation, this is plagiarism because you have directly copied the author's structure. In this case, a direct quotation would have been appropriate.