If not, you need to purchase one (Well really it is like renting your domain name for however many years you keep on renewing a domain name for, you can choose to renew yearly or you can pay upfront for years in advance). Some people may even ask, what is a domain name? Well it is the name that you see at the very top of a web browser. You know, like servertosite.com or domain names that end with other extensions besides the global .com, like the extension .net or country specific domain names, .com.au, .us, .be, co.il, .ca and there are many more domain name extensions you can choose from. My recommendations are .com and .net for most websites catering to a worldwide audience, .org for worldwide non profit or informational websites and your own countries specific domain name extension/s for websites audiences specifically in your own country or a specific country you need to make a website for (There may be a few choices of domain name extension for one country alone). Please note that some country specific domain names are only able to be registered by citizens of the specific country they refer too.
You find a domain name registrar that sells domain names for a reasonable yearly price and get one (You will also find many electronic market places that sell domain names). Next you will need web hosting or a full web server: Make sure your server or web host supports PHP, is based on Linux not Windows, runs Apache and has mod rewrite enabled. A huge amount of web hosts and servers have this configuration, if they don't have mod rewrite enabled, you can sometimes ask them to turn it on, but seriously they should have it on anyway, there is no excuse not too in this day and age. You will need to put the name servers from your hosting into the dns control section under the management console you will get when you make an account at your domain name registrar. You will have inputs available to enter ns1.nameservernamehere.com ns2.nameservernamehere.com. Web hosting commonly gives you two name servers. If you have your own server or VPS you may have four or six name servers, possibly more under your domain name, depending on how many IP address you have to spare. More name servers, means if some name servers fail you have backups to keep your site afloat.
Web hosting is were your website is stored and from where your website is delivered to its audience.
Your website package will be uploaded into your web hosting usually via a control panel called Cpanel or a different administrative like interface, this is software with a visual interface that web hosts install on their servers, so that it is easy for normal people to login and upload and manage their websites. You should hopefully be able to do this yourself once you have signed up for some web hosting.
Please make sure that you get the very common Linux with Apache server and PHP web hosting, with Apache mod rewrite enabled (Most web hosts should have Apache mod rewrite enabled already. but please make sure they can at least enable it, as they have no excuse except incompetence not to do that for you)
Remember to get the name servers from your web host if they are not shown clearly in your account somewhere (in Cpanel or other visual interface, even an email from your web host), as they are needed to put in the dns manager of your domain name registrar which is actually a seperate place and service from your web hosting, even though some web hosts may make it look as if they are the same thing. That may sound complicated to some, but really it is very easy.
Some people may also want to go better than web hosting and go for the more powerful and more secure option of a VPS or web server where the server can usually accept higher traffic to their website and or have multiple websites, due to more correct bandwidth allowances and dedicated RAM. A managed VPS or server is really the only choice for the non super geek (Remember you are getting pretty serious about your web presence when you enter this territory), I would personally go with quality managed VPS and server provider Knownhost for this, click here to visit Knownhost.
Unless you have your own server administrator to manage an unmanaged web server a managed server is the way to go.
KnowHost is a truly respected VPS/Hybrid & Dedicated server provider. Advantages of VPS over shared hosting: Dedicated RAM, Useable Bandwidth, Unlimited Websites, Shell, More Control.