How does NodeJS work?

I love JS (bet you have heard that several times before). So I have written some web apps (mostly in NodeJS), made things work, but I only know how to glue things together. As in, I can lookup for my required libraries on npmjs and glue them all together to work.

What now I am more interested in, is to learn how things actually work, the underlying theory.

I keep hearing some buzz words in Node community which I have no clue what they are but just know how to work with them.

So, I would really appreciate if someone can help begin with learning the theory behind NodeJS.