Hey there,
“こと” is translated as “thing, matter, fact”, but it seems to have other functions as well.
In this phrase, for example…
“日本のことでわから ないこと があったら何でも聞いてくださいね。”
… there´s a particle before and after “わから ないこと”, so it looks it´s part of the verb.^^
Does “not-understand thing” mean “not understand something”? “If you don´t understand something japanese, ask me anything you want please?”
I feel like I can´t figure this out on my own, so I´d be glad if someone could help me 
お願いします !
日本のこと “anything about Japan” could also have said “日本について”
わから ないこと があったら "if there is something (or anything) you don’t understand’
Japanese is full of redundant words . Words like かと or もの are often added for balance or fill in sentences. Japanese is a living vibrant and somewhat fuzzy logic language. You have to get used to it. It is best to not ask too many questions and to let your brain get used to it, and that will take some time. Enjoy!
“It is best to not ask too many questions and to let your brain get used to it…”
Sure
It´s just that I´ve “noticed” that koto-thing for weeks, so I was curious to find out what it means.^^
Anyway, thanks for you help
Thanks for the links
Have you ever heard of “thejapanesepage.com”?
Their explanations are not as detailed, but they´re less headache-provoking for beginners like me^^