The shell can be a complicated place, but hopefully by now you're starting to get a sense of how the pieces fit together. No one concept defines the Unix environment. Instead, Unix is something like a library of ideas. Many of them are old, dusty ideas, and most have at least a few sharp edges, but they tend to be in the library because they can be combined with each other to solve new and complicated problems.
This series will continue with specific projects utilizing the Raspberry Pi and other single-board Linux computers. In the meanwhile, if you haven't, you might want to check out the huge pile of Adafruit guides already available for the Raspberry Pi and the Beaglebone.