Kurantmünze is a fancy word for money that the government says is worth a certain amount. It's like getting 10 stickers for your good behavior - everyone agrees that 10 stickers are worth something. Kurantmünze is like that, except the government says how much something is worth.
Back in the old days, when we didn't have paper money or credit cards, people used to trade things like chickens or sheep for other things they needed. But it was hard to carry around a lot of chickens when you needed to buy something big like a house! So people started using coins made out of valuable materials like gold or silver.
This is where kurantmünze comes in - the government decided to make special coins that were made out of a certain amount of a valuable material and were worth a certain amount of money. So instead of having to carry around a bunch of chickens to buy something big, people could use these coins instead.
Nowadays we don't use coins made of gold or silver anymore, but we still have kurantmünze - it's just made of cheaper materials like copper or nickel. You can use it to buy things like candy or toys at the store. So just like how 10 stickers are worth something to you, kurantmünze is worth something to everyone who uses it!