Bode plots are a very useful way to represent the gain and phase of a system as a function of frequency. This is referred to as the frequency domain behavior of a system. This web page attempts to demystify the process. The various parts are more-or-less stand alone, so if you want to skip one or more, that should not be a problem. If you are only interested in a quick lesson on how to make Bode diagrams, go to "Making Plots." A MATLAB program to make piecewise linear Bode plots is described in BodePlotGui.
The documents are:
Also available is a compilation of items 1 through 8, for easy printing.