For products "placed in service" in 2012, you need to file the 2012 version of IRS Form 5695
and submit it with your 2012 taxes (by April 15, 2013).
On the 1040 form
you enter this tax credit from Form 5695 (the residential energy tax credit) on line 52.
Save your receipts and the Manufacturer's Certification Statement for your records.
Submit Form 5695 with your 2012 taxes.