You will need to register a domain ie: kissinggame76.com
Unless you intend to host your infrastructure yourself , you will need a hosting company, many different types of hosting plans are available, but for the very simplest Splunk installation, you'll want a single dedicated server(virtual or physical)
There are loads of companys that provide these services , godaddy.com are one such that will do the above for you.
Your domain name will resolve to your hosted server.
You can then install Splunk on your hosted server.