Blog post: Convolution of Signals: Why?
Convolution expresses the output of a linear time-invariant system in terms of the system's impulse response and the input. In this lesson you will learn a graphical approach to evaluating convolution. Learning how to interpret convolution graphically will develop your intuition for understanding how the impulse response characteristics impact the system output. For example, you can quickly determine where the output is zero, or whether it is increasing, decreasing or constant in certain time intervals. Understanding graphical convolution will prepare you to predict and analyze system behavior.
The first video introduces the graphical convolution method and the second video provides several detailed examples.