You enter the quantity of ETH you want and it will compute how much it would cost. Alternatively you could enter the level of fiat you want to commit. The platform will calculate how much ETH you will get. Learn a lot more about the denomination of Ethereum models. https://financefeeds.com/ifast-global-bank-launches-multi-currency-current-account-with-high-interest-and-cashback-in-the-uk/