Probability means you possibility to win the trade. Now the percentage will depend on your strategy and your risk reward ratio. It is not possible that you will win all the trade. If you risk reward ratio is 1:1, then you have to win more than 50% of your trades. And if your risk and reward ratio is 1:2, then you can be profitable even if you win less than 50% of your trades. So learning the risk management is very important in Forex. I took a course from XeroMarkets broker, there I learn a lot about risk management. I also like the brokers low spreads and minimum trade cost.