EURDUSD is much easier:
Let's say EURUSD = 1.3000. You want to buy EUR 1,000,000 worth of $.
You now you own 1,000,000*1.3000 = $1,300,000.
EURUSD goes to 1.4000. You decide to convert back to $.
$1,000,000*1.4000 = $1,400,000
Great trade! You made $100,000.