It is important to understand the building blocks of systematic investing strategies before learning how to build them. Here is a schematic from the book, Inside the Black Box - The Simple Truth about Quantitative Trading by Rishi Narang, that provides a good way to visualize these building blocks and how they fit together in a system.
The Black Box Revealed
The author had aptly titled it - The Black Box Revealed, since that is how most people perceive it to be from the outside.