The combination of radicals for this kanji may not be obvious at first, but if you look carefully you'll see it. The lid is inside the head for this kanji because it's holding something in. Imagine the top of someone's head being closed by a lid. Open that lid up and peer inside... it's full of yen coins, the currency of Japan!
What does the word yen sound like? It sounds like えん. Why? because back in the day, Japanese used to have a "ye" sound, but now it doesn't. Instead, it's an "e" sound, which is why yen = えん!