Hello, I am an international student in the US and I am going back to my country in a year. I want to buy and sell US stocks online (at Tradeking.com, Zecco, or scottrade) but I don't know if I have to pay taxes for my gains here. I mean, if I gained $5k for online trading, should I pay taxes here in the US or in my country. I don't know how taxes work in the US, only thing I know is that IRS collects it. So, what should I do before starting to trade online? PS. The websites ask your SSN and I don't have one.