Forgoing live and reaching out to your potential clients and viewers you just not need a domain name, you also need to register your domain name on some registrar, there is a number of registrars available where you can register your domain like Godaddy, Namecheap, and many more.
These Registrar charge you some money for the services they provide, those who provide the best service will charge you more.
You also need a hosting company where you will host your site, the hosting is basically a space required to place your file on the server, same as registrar their price is different for the services they provide, usually, those who provide more services they will charge you more, you can more about hosting at http://www.bluehostreview.co/bluehost-review/, but here is a list of hosting who are providing the best services at a normal rate.
BLUEHOST HOSTING
Load time: 427ms
Uptime: 99.99%
Cost: $2.75/mo
Support: Live Chat Available
INMOTION HOSTING
Load time: 813ms
Uptime: 99.93%
Cost: $3.99/mo (3-year plan)
Support: Live Chat Available
HOSTGATOR HOSTING
Load time: 424ms
Uptime: 99.96%
Cost: $2.99/mo
Support: Live Chat Available
GODADDY HOSTING
Load time: 448ms
Uptime: 99.95%
Cost: $2.49/mo
Support: Live Chat Available