Allright, you've created your first redirect, but then these DNS settings appear.
These changes are necessary for letting the internet know where to find the redirection service that you've just setup for this domain.
These DNS changes need to be made at your domain. In most cases, this can be done at your domain registrar. If you use external nameservers (Cloudflare for instance), you need to make the changes there.
You can find the nessesary DNS changes in your redirect.pizza account after adding the redirect, or see What DNS types can I use?
Unsure where your DNS is hosted? A good way to check this is to see where your nameservers point. You can check this with an online tool like WhatsMyDNS: https://www.whatsmydns.net/#NS/example.com
Made the necessary DNS changes? It may take up to 24 hours before these changes are fully propagated! Please be patient.