Well, since you can only set nameservers at your provider you need to setup nameservers on your own.
As far as I understand this, your provider only allows to set the nameservers of a domain. This means the following: if you open your terminal and run:
You'lle get a reply at the end with this:
Name Server: ns10.projektfarm.com
Name Server: ns30.projektfarm.com
Name Server: ns20.projektfarm.com
That's what a nameserver lookup does. It will not tell directly about zone and on what IP a domain is hosted, but it will just tell you which name server is authorative for a given domain name.
In a second step you can then query that name server to find out more about the zones for that domain:
dig @ns10.projektfarm.com howtoforge.com
And you'll get this reply:
; <<>> DiG 9.9.3-rpz2+rl.13214.22-P2-Ubuntu-1:9.9.3.dfsg.P2-4ubuntu3 <<>> @ns10.projektfarm.com howtoforge.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55998
;; flags: qr aa rd ad; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 0
;; WARNING: recursion requested but not available
;; QUESTION SECTION:
;howtoforge.com. IN A
;; ANSWER SECTION:
howtoforge.com. 180 IN A 22.214.171.124
;; AUTHORITY SECTION:
howtoforge.com. 180 IN NS ns10.projektfarm.com.
howtoforge.com. 180 IN NS ns20.projektfarm.com.
howtoforge.com. 180 IN NS ns30.projektfarm.com.
;; Query time: 14 msec
;; SERVER: 126.96.36.199#53(188.8.131.52)
;; WHEN: Sat Mar 01 08:18:20 CET 2014
;; MSG SIZE rcvd: 117
Now you know that howtoforge.com is hosted on IP 184.108.40.206
So, as said before, it sounds your domain provider only allows you to set the nameservers where the zone info can be found.
Basically for your own domain you can set it up on your VPS with zone file and so on. BUT you also need to setup your VPS as a nameserver and then tell your domain provider that your domain is hosted on the nameserver on your VPS.