Getting a Domain Name
Before you can connect your server to the World Wide Web and access it through a Web browser, you will need a domain name. This address will be used to generate the SSL certificate that web browsers rely on to create a secure network connection and verify we are who we say we are.
Domain Registrars
https://porkbun.com/products/domains
https://www.cloudflare.com/products/registrar/
You don't need to pay for an SSL certificate, they are generated for free.
Domains can be purchased from a variety of domain registrar, such as Namecheap, Domain.com, and NameSilo. They vary in price based on their desirability and expected popularity. There are also services like MicroDomains that sell domain names that are 5 characters or less. Some are very affordable. These are great for making services available for your services remotely.
Dynamic DNS
Duckdns, no-ip, freedns, router brands