How can I learn about CS?
Here are a few books I recommend:

Discrete math: Concrete Mathematics: A Foundation for Computer Science, Don Knuth. (http://www.amazon.com/Concrete-Mathematics-Foundation-Computer-Science/dp/0201558025). 

It's very complete and also pretty approachable for someone without much of a theoretical math background. 

Algorithms: Algorithms, Kevin Wayne and Bob Sedgwick. Again, very complete and presents all algorithms with motivation and extremely well-written Java code. There's also a really good website with a lot of the info available for free (http://algs4.cs.princeton.edu/home/). 

Systems: Computer Systems: A Programmer's Perspective, Bryant and O'Halloran. This one is a little more dense than the two above, but it's a great resource if you know what you want to learn about (e.g. processes, floating point arithmetic). (http://www.amazon.com/Computer-Systems-Programmers-Perspective-Edition/dp/0136108040)

I've had experience with all of these at the undergrad level, so they don't require an enormous amount of experience or higher-level coursework.