Derrida's "Structure, Sign, and Play in the Discourse of Human Sciences" is an extraordinarily important essay in the post-structuralist movement. It highlights several major theoretical principles of deconstruction.
First, the essay questions the idea of a transcendental signifier. It asserts that the principles that provide the basis for thought in Western culture are themselves merely useful theories we cobble together, not unalterable, transcendent truths. Derrida uses as his main example in the essay the nature/culture binary. Separating aspects of life into two distinct categories as either natural or cultural is useful, but it is not absolute: some things, such as the incest taboo, are both natural and cultural simultaneously. Foundational methodologies we use to interpret the world, are, therefore, Derrida asserts, themselves simply human constructs. They are useful, but like a bridge we might cobble together from spare parts to cross a river, they are not eternal or inviolable: if a bridge starts to have holes we can fall through or we find a way to build a better bridge, we should do it and not simply hang onto the old.
Second, because the foundations on which we build knowledge and understanding are human constructs, we don't have to take them with the utter seriousness of immutable divine principles: we can play with them, have fun with them, and be creative. This sense of jouissance, joy and play, is integral to post-structuralism. We can own a certain sense of freedom over cultural constructs.
Finally, because the essay takes apart a binary construct—the nature/culture divide—it created an environment in which deconstructing binary oppositions such as male and female, black and white, and inside and outside became a major focus of deconstructive practice.