Estimated tax online payment

[KTD]

If I pay my estimated tax online on http:www.irs.gov/payments.

Do I need to also send any documents (physical paper copies) like voucher or 1040Es or anything else to IRS office?

How will IRS know that its me who is paying the tax?

Do I make estimated tax payment seperately for federal and state?

[tagteam]

You do not have to send any documentation to an IRS office when using Direct Pay.

The IRS requires you to verify your identity which requires, among other things, your name and social security number.

Federal and state are completely separate. You need to visit the web site of the taxing authority for your state (e.g., department of revenue, franchise tax board, comptroller) for further information.