IMHO, reading isn't enough, you must do it and experience issues that makes you go "what? How?".
But your question is so vague that there are a lot of answers.
There are a lot of stuff that can be considered big concepts : basic electronic, networking, OS, peripheral communication, compilers, language, algorithms, assembly/procedural/object/functional programming, and the whole world of "AI".
What do you want to know?
- why you shouldn't call .where() a million times in linq?
- how internal statistics tables are managed in Sql server to produce the execution plan, how to watch the execution plan?
- big endian vs little endian?
- how to use telnet to get an HTML page from a web server?
- why everyone thinks that their favourite language is the best?
- why is the first char in a string in pascal at [1] when its at [0] in a lot of other languages?