please advise how to make a server with dynamic ip

[julian]

please advise how to make a server with dynamic ip
my net provider, gives me a free DDNS so I could have fixed ip,
but do not know how to set up and put that subdomain ex. hidem.go.ro,
they told me that I should not make any changes to roter or computer, but the server must do something and do not know what to do, please tell me please excuse me my English