I have held the domain cookieswork.co.uk for years without doing much with it so I decided it would be good to setup a custom domain for these github pages. I started by following the steps in githubs documentation
After loging into my domain provider I edited the DNS settings to create a CNAME forwarding to cookiesworld.github.io. A CNAME is a canonical name, which is a fancy way of saying its an alias for another address.
I then went to the pages section of settings for the repository and entered the custom forward. Github does a lookup check which trakes a short while then after a couple of refreshes my pages my site moved to the https://blog.cookiesworld.co.uk