Link a domain to an IP adress

Hi there, i just bought a domain on OVH and already start developing my app on a DigitalOcean server.
Si I have a domain and an IP. How do I link those two together ?
I'm completely lost in all this DNS matter.
I have put the IP in the "DNS Servers" section (with ns104.ovh.net & dns104.ovh.net), but it doesn't seems to work.
At this point, if I try to go on the site through the domain name i get a 500 error, but with the IP it work correctly.