You didn’t!!! Not at all!!
Well, I try to be methodical…And there isn’t a “single answer” what I did was learn a bunch of things over time. Some of my approaches were: Going to a catholic library (several actually) and really browse all the shelves until I had a grasp on the division and different kind of contents they offered. Also looking through publishers catalogs on their sites gives a good idea of the different “categories” they classify their books under.
Then, I was actually curious to find out what a college degree in “Philosophy/Theology/Religious Sciences” actually looks like…So I checked out the sites of some of those degrees and saw how the courses were structured and divided the body of knowledge among them.
These two approaches take some time, then actually reading a book of each…For example, “canon law” is basically the “legal stuff” pertaining to the church. Then “moral theology”, “hagiography”, and so on…
The main part is of course “Sacred Scripture” but at some point I wanted to explore other things so I would get other views…
Some parts are very formal like “canon law” and “liturgy”. I find “Latin” an interesting long term goal for myself, but will skip “Greek” or “Hebrew” (you can’t know everything)…
Also depends on my free time, if I have more free time I go into “heavier” readings, else I read “lighter” books like “hagiography” that adds to general culture and always provides some insights. Lately, I focus a bit on the fun part, and read whatever I find more appealing at that moment. It probably helps that I am constantly reading over 10 books at any given time…
For a general overview I enjoy John Hardon S.J. works:
http://www.therealpresence.org/archives/archives.htm#nav