What does 14K NH and the NH letters are directly together inside ring mean?

Well, darling, "14K" stands for 14 karat gold, which is the purity of the metal used in the ring. As for "NH" being directly together inside the ring, it likely represents the manufacturer or jeweler who made the piece. So, in simple terms, you've got yourself a 14 karat gold ring made by the NH company. Congrats!