So I am 2nd year now and we started this new course Theory of Signals. Already I bumped into a wall when it came to understand basic stuff. Here is what I mean [PLAIN]http://pokit.org/get/0864633c869b647116b980428a07d4f1.jpg [Broken] Here we have 4 functions, each representing one type of signal. 1st one I understand. Its a continuous function, defined at every point. 2nd one reminds me of a plotted sequence. But the thing that confuses me is that vertical line connecting abscissa and the value of the signal. Does that line represent something? Or is it just for visual purpose? Same question for the 3rd graph. It is even more confusing. It goes zig-zag. Again what do those vertical lines connecting 2 parts of graph represent?