What part of tikz manual to read for contour integral plots

I am looking to plot a number of contours in the complex plane using tikz, but I do not know what part of the manual I should read. I know very basic tikz, but am hoping someone can direct me to a place in the manual that can help me learn how to plot a number of different contour diagrams.

For example, is there any part of the tikz manual that will show how one can plot the contour shown in this link? I think it may have to do with "loops," and if this were the case, are there any "pre-requisites" to learning "loops"? Or where in the tikz manual might I learn how to reproduce a code similar to the one seen here? Any comments or answers are helpful. Thank you!