DNS problems when using Free Tier Oracle Hosting

I'm new to hosts and domains & an running a university project on the free-tier oracle hosting. Now I'm wondering if i should have used the free tier of AWS?

context: I have a server in oracle running ubuntu, I am trying to create a wordpress site using docker-compose and a tutorial, for the tutorial I needed a domain so I bought, the problem is that I don't know how to link it to my oracle vps. I already tried using custom dns (ns1.mydomain.site) pointing to my public ip and it didn't work