Buying and selling shares has nothing to do with FOREX. Forex is very dangerous, and addictive. One shouldnt get too excited about it or addicted to it. Yes you can make lots but you can lose all your money instantly.
The problem with it is that it depends on margin trading. Ive researched this and couldnt find much info on its permissability in Islam. Some gave their opinions but I personally feel that its not with a good understanding of how it works.
But their evidence seems to be strong, however. They say it involves Riba for two reasons :
1- Interest in whatever form is paid for margin trading.
2- On the basis of the rule "Every loan that brings benefit, is Riba"
Ive seen some (FOREX experts, not sheikhs) argue against the second, saying that SOME brokerage firms, arent the same people who give you the extra money to trade with, so theres 3 parties involved in SOME cases.
I dont know the ruling, im just stating points I read about. Also theres the issue of getting this loan (margin) but not really being able to use the money the way you want. So in this case is it really a loan? Is there anything wrong with that in Shariah? I dont know.
Buying and selling shares in the stock market is perferctly halal, providing that one follows certain guidelines (like avoiding buying shares in interest-based banks etc)