I've been programming for around... 6->8 years, and I've begun to realize that I don't really know what really happens at the low-ish level when I do something like

int i = j%348

The thing is, I know what j%348 does, it divides j by 348 and finds the remainder. What I don't know is HOW the computer does this.

Similarly, I know that

try
{
 blah();
}catch(Exception e){
 blah2();
}

will invoke blah and if blah throws, it will invoke blah2... however, I have no idea how the computer does this instead of err... crashing or ending execution.

And I figure that in order for me to get "better" at programming, I should probably know what my code is really doing. [This would probably also help me optimize and... err... not do stupid things]

I figure that what I'm asking for is probably something huge taught in universities or something, but to be honest, if I could learn a little, I would be happy.

The point of the question is:
What topic/computer-science-course am I asking about? Because in all honesty, I don't know.

Since I don't know what the topic is called, I'm unable to actually find a book or online resource to learn about the topic, so I'm sort of stuck. I'd be eternally thankful if someone helped me =/