I don't have much knowledge about forex trading, but still I'll try to share with you what I know.
Basically, forex trade needs huge investment to start earning money. First of all, to start trading, you have to deposit some amount in the website where you want to start. Usually the deposit costs more than $25. And then you have to buy again any currency in dollars and there is no limit for that. But more you invest, the more you gain. You have to sell that dollars for some other dollars when the value of your currency increases, and thus you can gain profit. But in case if the currency you have bought lose its value, you will have to suffer huge loss.