When looking for a hosting solution for your web site you'll discover you have the choice of shared or dedicated hosting.
Shared hosting is what it says it is. Your web site shares a server with other web sites. You don't have access to the other web sites files, they don't have access to yours and you don't share a domain name. What you do share is the machine and the scripts that are pre-installed on it. Why would you do this? Because it's cheaper.
The cost of setting up a server machine is not inexpensive. Even relatively large web sites are only a few hundred megabytes, so today's computers with multiple hard drives are easily able to handle the space. There can be as many as one or two hundred web sites on a shared server.
You'll find there are different platforms available in shared hosting too. You will find Unix/Linux or Windows NT/2000 as your platform. You don't have to choose the platform your PC is running. This has nothing to do with what the server needs to operate on. Unix platforms are very stable and are perfect if you have a site using mostly HTML pages, PHP or CGI. If you are using scripting such as Active Server Pages, have designed your web site using FrontPage, or need access to a Microsoft Access or SQL Server database, you need a Windows platform.
Shared hosting usually comes with a heap of extras and most are included in the price. You can get email, auto-responders, pre-installed scripts including counters and mail scripts, password protected directories, your own cgi-bin, and browser based control panels, secure directories and more.
However, if you need complete control of your server, you need a dedicated server. Obviously if you're not going to share the server with anyone, it is going to be more expensive.
Dedicated servers are usually only required by experienced developers. If you're not sure if you need a dedicated server, then you probably only need shared hosting.