This knowledge comes from reading different articles about forex , forums are also best option to get basic knowledge and views about trading. After investing some time in trading practice trader can get idea of market hat will be the first step towards successful trading. I think one can know from his own manual trading the experience he gets it is very useful for starters.You should have some knowledge and experience before starting a trade on the forex market. This market needs these two things a lot. You can get these two things by consulting the expertise and successful traders. Also you can get some knowledge about different forums having a lot of knowledge on forex trading.