For 2023, you report the expenses on form 5695. You are not required to attach proof, but keep your proof with your records for as long as you own the home and 3 years after you sell. (In future years, you will be required to enter qualifying product numbers on your tax return but that is not required for 2023.). The maximum credit is $600.
Be aware that for windows, you can only claim the cost of the window, you can't include installation costs. Try and get an itemized bill from your contractor as your deduction could get denied by an auditor if you can't prove the cost of the windows. Also, the windows must meet the "Energy Star most efficient certification requirements" in effect at the time of installation. You will want to keep proof of this as well.
Lastly, remember that the credit reduces your adjusted cost basis when you sell the home. For example, if you paid $100,000 for the home and paid $5000 for new windows, you would use a cost basis of $105,000 when determining your capital gains tax. But if you received a $600 credit, that reduces your cost basis accordingly to $104,400.
