To understand circuits, you really have to become familiar with some common building blocks. When I saw this circuit, I didn't think "okay, a couple resistors i

To understand circuits, you really have to become familiar with some common building blocks. When I saw this circuit, I didn't think "okay, a couple resistors in a configuration"; I thought, "oh, a voltage divider." So read up on voltage dividers, RC circuits, pull-up and pull-down resistors, and diode current-limiting resistors. Google them right now and start reading. That will make you dramatically better equipped to understand real-world circuits.