Is this at home, or are you using it from a hosted provider?
If it is at home, you’ll need to use what is called a Dynamic DNS service to hook it up to a regular domain name. (see https://www.dyndns.com/services/dns/dyndns/ for more info)
If it is a server provided by a web hosting service, talk to their support on how to register a domain name with their servers.
Honestly, this question has nothing to do with WordPress, and everything to do with web hosting. I don’t say that to be rude, but rather to let you know that the folks on this board don’t have any of the information that you’ll need in order to be able to guide you through that process.
Posting the question here is a bit like asking a tire manufacturer why your transmission doesn’t work. ?? hehe No harm done though – I’m just trying to help you get a quick answer.
Best of luck to you…
Cheers,
A