Here are a couple of good documents to read.
http://www.flightsimbooks.com/flightsimhandbook/
http://www.atpflightschool.com/students/downloads/ATP-Cessna-172-Training-Supplement.pdf
I will tell you, not long after "just flying around" for a while, I quickly realized how complex the world of flight is when I asked myself "OK, now how do I know where I'm going?", somewhat like you are doing. For every question, there is a Google answer and probably a few good YouTube tutorials, either real or simulated. All I do is investigate using these all these resouces when I need to learn something new, and then piece it all together.
The complexity of it all is what makes this so compelling, IMO. I learn something new pretty well every day and I'm still just trying to become half-decent at the basics of flight and navigation with the Cessna 152!
Have fun!