How to learn or do something complex?

Nothing in the world is complex if you break down into the bits and pieces that made it. What you see as a complex thing is a person or multiple persons spending a lot of time adding more pieces on top of a very simple design. So the easiest way to do or learn something complex is to learn the basic first and try to build something your own. Once you are on that path you will see how a simple thought or design evolves in complexity as you stabilize your design to cater to a wider set of uses.