In the business of trading,money management is to invest in that way that even if the market moves to worst position that's posible u dont loose your account and end up with nothing. they say only to invest 5-10% of your trading capital for a particular trade. before doing that u should calculate the range of the market within which the currency of your choice fluctuates. then u should assess and see the no of lots u can open according to your trading capital so that even if the market moves to the lowest point your account dosent close automatically.Thats the formula of money management.