Whenever I’m learning a new subject, I look for distinctions. These are concepts that are key to understanding the subject space, and which stand in opposition to each other. For example, the following distinctions are useful for understanding systems:

General Specific
Holism Reductionism
Open Closed
Dynamic Static
Outside Inside

There are more, but tackling these few can help you gain a foothold on systems as a subject. Some of these pairs are characteristics of individual systems. (I.e., you can talk about whether a particular system is static or dynamic, open or closed, etc.) Others are useful in understanding the field as a whole. (I.e., the distinction between reductionism and holism speaks to the usefulness of systems thinking in general.)

Distinctions such as these allow us to understand abstract concepts more clearly, much as the interplay of shadows and lights help us see objects in the physical world. They turn up the contrast in otherwise difficult subjects, helping us see their edges. However, as we dive into dividing subjects up into opposites, we must remember they describe a whole, and complex subjects often contain self-contradictions that resist easy categorization. (Of course that, too, sets up a distinction to be examined.)