I want to know more about combined words like "nitty-gritty", which consist of 2 words and hyphen, and means completely different thing from its parts. Could you show me more examples like this? And if you have time, could you explain me why it does mean different thing?

Zobacz tłumaczenie

I think the English term for what you're talking about is a "hyphenated compound." Searching around for that might get you more examples. But it's not something most English speakers notice. It's an interesting topic but it's not something I'd thought about in depth before.

Like オノマトペ in Japanese, it's not very easy to completely explain, and it's usually more casual. It's more something you'd get a "feeling" for.

As for when to use hyphens ("-"), there aren't easy to explain rules either, it's just something you have to learn like a lot of English spelling. When you take two words and put them together to make a new word, sometimes you use a hyphen, sometimes you don't.

EDIT: Another word that might help you is "reduplication." This is a phrase for rhyming words like nitty-gritty. Such as chit-chat, criss-cross, knick-knack, zig-zag, super-duper, etc.