How do you find bugs?

Question

I've heard about bugs like on Mr robot I was wondering how

Answer 1

If you mean bugs in your html/css/js code, there's no bulletproof way to do it. Syntax errors are easily eliminated by validating your code at:
validator.w3.org.
The tuffer part is when the syntax is correct but the fault lays in HOW to do things. Asking at Stackoverflow.com "what's wrong with this code?" can be a good idea.
(If I'm way off, it's because I haven't watched Mr Robot :).