I am an international student on post completion OPT.
(My student visa is still valid)

I work at a startup.

I did not fill any forms while starting work, and get paid monthly without deductions.

*If* I qualify as an independent contractor,
(1) Do I have to pay quarterly taxes?
(2) This would be my first year as an independent contractor... I think I read somewhere that in your first year maybe you can pay a yearly tax?. (not sure about this)

I haven't received any forms yet from the firm.

Thanks a lot,
Abhishek

Additional info: The startup I work for is an llc

You are independent contractor. You will report your income and expenses on schedule C or C-EZ (Form 1040). Then you put net income (or loss) on line 12 of Form 1040.

In your case the income is not subject to SE tax at 15.3%. Read about estimated taxes: Your U.S. Tax Return: Tax Filing by Self Employed Sole Proprietor or Independent Contractor

Thanks.

On the link you provided, it says you are exempt if you are a non-resident F1 student.

I am an F1 student so of-course I am a non-resident. BUT, there is something like "resident for tax-purposes"... so do I have to look into that, or am I good.

On F1 you are nonresident for 5 years. You must file nonresident tax return.
Read: Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents

To be specific, you will reprt your income on Schedule C and Form 1040NR. Since you are likely exempt, you need NOT complete Schedule SE because you are NOT liable for self-employment taxes.

Thanks... but by June 15 I only need to fill schedule c... right?
I suppose 1040nr is for April 2010?

You CANNOT submit Schedule C by itself; it must be attached for a Form 1040NR.