The concept of integrating along a square?

I had a question;

What is the idea (in complex analysis) of integrating along a square? Take a look at @M.N.C.E.'s method on Evaluate $\int^1_0 \log^2(1-x) \log^2(x) \, dx$

I am not quite sure what the person means by integrating along an infinitely large square?

Can someone tell me where I can find more information about this? I don't have a lot of experience with complex analysis, and would like to learn about this method of squares etc.. and residues.

Help is appreciated!

• It's not "the method of squares". That's what he chose as a contour. – UserX Nov 10 '14 at 17:28
• you choose an contour of integration which looks like a square and let the length of two or all four of it edges go to infinity. The second choice is in many cases equivalent to choose a infinitively large (semi)circle. – tired Nov 10 '14 at 17:38
• The easiest ways to learn complex analysis are probably: by a course, by a book, or by a video series. (I don't know if multivariable calculus is a prerequisite; I don't know complex analysis yet.) – Akiva Weinberger Nov 10 '14 at 17:47