If you'd like a very simple and quick introduction to systems thinking, here's a good summary.

Excerpt:

Why Is Systems Thinking Important?
Why is systems thinking valuable? Because it can help you design smart, enduring solutions to problems. In its simplest sense, systems thinking gives you a more accurate picture of reality, so that you can work with a system's natural forces in order to achieve the results you desire. It also encourages you to think about problems and solutions with an eye toward the long view -- for example, how might a particular solution you're considering play out over the long run? And what unintended consequences might it have? Finally, systems thinking is founded on some basic, universal principles that you will begin to detect in all arenas of life once you learn to recognize them.

The article: The Systems Thinker Newsletter