To use your registrar (or hosting provider) nameservers, DO NOT change the nameservers in your registrar DNS management tool. They MUST remain with ns1.your-registrar.domain, ns2.your-registrar.domain, etc... Change only the "Zonefile" records content.
While you are using your registrar nameservers, you can stop the dns service (bind9) and close port 53. You can also disable the DNS config plugin from Admin / Module Admin. You will still need to create the domains under Domain Management / Domains in order for Apache to be configured correctly with the virtualhost settings and to be able to create new mailboxes for that domain. However, you do not need to create a DNS records (A, CNAME, MX etc.) under the DNS Manager in Sentora.
When you bought your domain from a registrar, it will more often give you a nameserver configured by default to resolve your main domain to some parking servers or to its own default servers for email, blog, etc. You will have to setup both your main domain and your Sentora subdomain (and any subdomain you want to use). You have to login on its nameserver management and then setup IP of your server
1) Setup the main domain A or AAAA master record (use A record if your server have an IPv4, else use AAAA record for IpV6). Ensure that there is only ONE master record, the most often named "@" that point to your server IP.
2) Setup the Sentora subdomain you given while installing Sentora at FQDN question. Usually, this subdomain is setup as an alias with a CNAME record that redirect to @ record or to you master domainname record. But you can also create a A or AAAA record for it.
3) Check that all other subdomains already present (always : www, the most often : ftp, mail, smtp, webmail, blog, etc. )
-> If you will host the same service, check that the subdomains points to your server (with CNAME @, CNAME masterdomain or A/AAAA IP).
-> if you want to use your registrar service (some provide blog, etc tools) leave it pointing to your registrar servers,
-> else if you do not want the subdomain to be reachable delete the record. (By default, a subdomain present on your name server but not created on your server will display the Sentora login page)
WARNING : avoid using the wildcard subdomain " * " unless you really know what you are doing. This is out of the matter of this little tuto.
After changing some DNS, let enough time for DNS propagation or use propagation test tool. More Info here.
If you bought your domain name from your server hosting provider, it generally have already configured the DNS server that resolve your domain with the right IP and default subdomain (step A -1 above).
You will have only to create the subdomain corresponding to your Sentora access (step A-2 above), and check that other subdomains are ok (Step A-3 above)