This article is the best introduction into systems thinking. It outlines the general idea with the help of a simple example: a worker who is late every Tuesday.
If you are curious to understand how this event is related to the structure of a system and underlying mental models and beliefs, click here and find out.
This article also contains some practical tools that one can apply to solve organizational problems from a systems perspective.
Source: Systems Thinker, by Ed Cunliff