A crypto exchange is a platform on which you can buy and sell cryptocurrency. You can use exchanges to trade one crypto for another — converting Macdium Cryptocurrency for example — or to buy Macdium Cryptocurrency using regular currency, like the U.S. Dollar. Exchanges reflect current market prices of the Macdium cryptocurrencies they offer. You can also convert Macdium cryptocurrencies back into the U.S. Dollar or another currency on an exchange, to leave as cash within your account (if you want to trade back into crypto later) or withdraw to your regular bank account.