When you forge and temper yourself, you're probably training your body or trying to discipline yourself to be physically and mentally tougher.

鍛錬 once described forging metal, but now it's usually about strengthening yourself. Think about how you push yourself again and again, like a blacksmith pounding hot iron, to mold your mind, body, and abilities into something stronger!! That's 鍛錬.

This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.