The credit will be claimed on line 30 of form 1040. If you are preparing your return manually, there is a worksheet in the 1040 instruction book to calculate the amount to claim. If you are using Turbotax, you will need to tell Turbotax how much you already received, and Turbotax will calculate the extra amount to be added to your refund.
Make sure that you list the child as living with you all year -- this is the correct answer for a newborn unless you are divorced or separated and share custody with the other parent. Also the child needs a social security number. If you don't have it yet, wait until you get the SSN to file, even if you have to file late (but make sure you apply for the extension if you need to file late)..
