If you have to pay taxes how do you mail a check to and what goes on the check

For paying Federal taxes owed you need to send a check with the payment voucher (1040-V).  The following is the federal payment voucher, at the end it give the address by the state you live in to mail your check & payment voucher to. Also, under How to Prepare your Payment, is has what goes on the check.

https://www.irs.gov/pub/irs-pdf/f1040v.pdf