Currencies are traded in lots. A standard lot is 100,000 currency units. A mini lot is 10,000 currency units. And, a micro lot is 1,000 currency untis. For forex beginners, it's a good idea to trade in micro lots so that your losses are smaller.
So, if somebody says "I am long in EUR/USD with two mini lot", it means he has bought 20,000 euros.