DNS is a phone book. Cloudflare’s just happens to be very fast. A Registrar tells the world where your phone book is. And your phone book needs all the entries, including mail and web server addresses.
It just so happens that your registrar is also your authoritative DNS. But if they tell the world to use Cloudflare DNS instead, it’ll be faster, and have all the information your current Netsol phonebook has…as long as you make sure Cloudflare has all the DNS records that Netsol has.
Cloudflare queries for IP to automate the population of Cloudflare DNS. It’s a one-time process. After that, you need to make sure it got everything, then you’ll no longer use Netsol DNS for your domain. But your domain registration will stay with Netsol.