When we trade forex we are not actually buying or selling currency. We are placing a bet which way the exchange rate between two currencies will move.
So if you “buy” EUR/USD at 1.3001, you are betting that the exchange rate will rise through 1.3002, 1.3003, 1.3004 etc. The effect if your bet is parallel to the effect on your account if you actually owned some EUR. But remember that you have not bought any EUR, you did not sell any USD to get them and no matter how long you leave the position open or how high the exchange rate goes, you will not receive a bundle of EUR. What you will receive is a payment from your broker in proportion to the amount you placed your EUR/USD bet with.
The payment into your account will be in the same currency you opened it in - if your account is in USD, the payment will be in USD, if its in JPY the payment will be in JPY etc.