https://www.gov.uk/get-free-childcare-if-youre-working I find it all pretty confusing but this timeline thing might help?
When you apply you get a code to give to the nursery and you have to reconfirm your details every 3 months, our nursery gave us a form to fill out too so I’d speak to the nursery if you’re unsure about anything they should be able to help
Hi commenting to see the answer as I am same x