DNS Nameserver Help

Please, I’m struggling to understand the difference between the two DNS configuration: Create Nameserver and Config Default Nameservers.

I have connected my CyberPanel to Cloudfare and have a WordPress website hosted but when I checked using MX Tools I can see that tye website has four (4) NS two of which points to my server with no IP and the other two to the registrar NS and IP.

How can I secure the domain from DDoS using Cloudfare?

default is for the every domain like if you add default that will be available for all domain s

So with default, new website uses my panel NS but what is the other one used for?

Also, creating the default requires having two NS with IP, is it that they uses the same IP and what IP is expected to be there, my CyberPanel right for the two?