In order of occurrence, Tubal-cain is the last son of Lamech mentioned in Scripture. While Lamech's first two sons (Jabal and Jubal) came through Adah, Tubal-Cain came through Lamech's other wife, Zillah:
As for Zillah, she also gave birth to Tubal-cain, the forger of all implements of bronze and iron; and the sister of Tubal-cain was Naamah. (Genesis 4:22)Not only was Tubal-cain the forger of all implements of bronze, but he was also the forger of all implements of iron— an amazing feat. It also seems likely that he was a major contributer to the invention of forgery— but if he was not the inventor, he greatly advanced the usefulness of the trade.
In this verse, the word implements seems to be used because of the many different items that can be forged from bronze and iron. While many useful tools were likely created from these two materials, the materials were also likely used to improve and upgrade weaponry— for it would be absurd to think that there was no war prior to the flood (see The Pre-Flood World: Filled With Violence). Of the very first two brothers, did not one slay the other?
As for Tubal-cain's sister, Naamah, nothing else is mentioned of her in Scripture. Commentators suggest a number of ideas on the subject— everything from the idea that Naamah was Noah's wife to the idea that Naamah was a wicked woman who led the world astray. John Wesley seems to sum it up best in his commentary when he states, "Why Naahmah is particularly named, we know not; probably they did, who lived when Moses wrote".
Lamech's Song - Genesis 4:23-24
The Father of Musical Instruments - Jubal - Genesis 4:21
The Pre-Flood World: Filled With Violence (Part 1) - Genesis 6:11-13
Cain and Abel: Two Routes - Genesis 4:1-2
What Does the Bible Say About Polygamy? (Part 1) - Genesis 4:19