Q: "What's the difference between brownies and chocolate cake? Texture, taste, method of preparation, what? I haven't tasted brownies before and too lazy to try to make one."
A: The critical difference is that brownies are unleavened -- they contain no baking powder or soda. The lack of leavening, and minimal amount of flour, results in a dense, chewy bar.
Note, some recipes do call for leavening and result in something that's really just a chocolate cake. I don't know why people bother to make such things, I don't know of anyone who prefers "cakey" brownies to "chewy" brownies.