Thanks a lot madcaptenor. This totally makes sense now. And what happens if I start for example in January 15, this means I'm only responsible for 3 months until April 15 right?
Also what happens when I'm absent for example for say 2 months (March,April), can I do it later?
also, you can file an extension if you don't owe money. you can use an online service to help or there are tax preparerors also. but you can probably file it your self or online.
You can file for an extension on the paperwork even if you owe money, but you need to send a payment (based on your estimate of what you owe) with your extension application, since the money is due on April 15th whether you get an extension or not. (If you significantly underestimate what you owe, you'll be charged a penalty plus interest.)
Also, to clarify what others have said: If you start work in January 2016, you will not need to file taxes in April 2016: the April 15, 2016 filing date is for taxes on income in the previous year (January - December 2015). For income earned in 2016, you'll need to file taxes by April 2017.
"Now I'm going to work for a new US based company and the salary is six figures."
This sounds like you'll be a regular employee of the company, which is what all the people who have replied here are assuming. However, if you're going to be paid as an independent contractor (taxes reported on a 1099 form rather than a W-2), the tax situation would be entirely different: the company won't withhold taxes and you'll be responsible for making quarterly estimated tax payments.
The agency in charge of U.S. federal taxes is the IRS, and they have a huge amount of information on their web site, http://irs.gov, ranging from very basic introductory stuff to the most detailed information for accounting professionals. Every state also has a similar web site for their state income tax.
Also what happens when I'm absent for example for say 2 months (March,April), can I do it later?