How do I add the domain I own in oracle cloud and host it live?

Unfortunately, there's no simple answer to your question. The general documentation on using Oracle Cloud DNS Service can be found here. Below is a quick summary of tasks that need to be completed:

1. Note the public IP address assigned to your compute instance that's hosting the web server. Assign one if necessary. The compute instance must be on a public subnet to be assigned one.
2. In your tenant's root compartment, create a Zone for your domain, e.g. example.com.
3. Create an "A" zone record, e.g. www.example.com => 123.123.123.123
4. Publish the record.
5. On your Registrar's DNS management console, update the name server records to point to Oracle Cloud's name servers assigned to the zone.