I am F1 OPT student working in NJ,what all taxes are applicable to me.After taxes how much salary will I get per month if I am paid 30/hr on W2.

How long have you been in the US and where are you from?

I am here since 2010 just graduated in May 2012.

From India

You will be liable for INCOME taxes on the federal, state and possibly local level.

However, you are exempt from FICA (Social Security and Maedicare) taxes. MAKE SURE your employer is aware of this. If he wants proof, refer him to IRS Pub 519, pages 51-55