Your Health Visitor at your GP Surgery should be able to give you all the information you need.
There are local differences, for example, in Scotland the children go to school in August. of the year in which they are five, not four.
Make sure you apply by the deadline, if you don't they won't automatically give your son a school place and you might lose out on the school you want. If you already have a school in mind, ring them up and ask what the local procedure is.
the best way is to find your local schools and ask to visit them thay will give the advice how to apply and look on local council web site to find the best school in your area and look up there results on the web good luck