What is the meaning of Nitty-Gritty?

Tweet

I just came across this word, and I don't know the meaning of this world at all. I was trying to get my personality facts by my name, and the word Nitty-Gritty I've found in the results. The full sentence with this word was: "You are secretive, self-contained, and shy. When it gets down to the nitty-gritty, you are an expert. You know all the little tricks of the trade, can play any role or any game, and take your love life very seriously." Can anyone help me to understand? Happy myLotting!