Hi and welcome to Just Answer!If you are neither US citizen nor a resident of the US - for income tax purposes - you are a nonresident alien.If you are a nonresident alien - you are taxed ONLY on income from US sources.
There are some complex rules to determine the source of income. You may take a look - page 12 IRS publication 519 - http://www.irs.gov/pub/irs-pdf/p519.pdf - Table 2-1. Summary of Source Rules for Income of Nonresident Aliens.
it does not say anything about sale of shares etc so should I Presume I don't have to fill any form for IRS if I make Money from selling shares. However it does mention Dividend. But I think My broker deduct tax for any dividend paid.
Thus if you have a gain from sale shares of US corporation - that is income from US sources and is taxable in the US. If however - that is the gain from the same of foreign (not US corporation) - the gain is not from US sources and is not taxable for nonresident aliens.
Similarly are taxed dividends - however the US-India tax treaty will apply. See page 13 - http://www.irs.gov/pub/irs-trty/india.pdf - ARTICLE 10 Dividends.According to that article - dividends generally may not be taxed more than 15%.
Also the tax treaty allows each country to tax gains of nonresidents - see page 18 - ARTICLE 13 Gains -- Except as provided in Article 8 (Shipping and Air Transport) of this Convention, each Contracting State may tax capital gain in accordance with the provisions of its domestic law.
To claim any tax treaty benefits - you need to provide a signed form W8BEN to your broker.