A domain name is a unique name used to address things on the Internet. Examples of domain names are wikipedia.org, google.com, and bbc.co.uk. See here for a fuller description.
When you have a domain name (for example yourname.com), you can use it for email (as in fred@yourname.com) or for a web site (as in www.yourname.com).
You obtain a domain name by registering with a domain name registrar. Your domain name will cost from a few pounds a year.
There are companies called ISPs (Internet Service Providers) who run computers which are attached to the Internet and which run web sites. You need to sign up with an ISP; they will provide you with a user identity and a password so that you can manage your web site. (In most cases, you can register your domain name via your ISP.)
ISPs are very variable in the prices they charge and, more important, the service they provide. 'Service' is a matter of reliability, and the way the ISP handles problems if they occur. Do not assume that larger is better in the context. Some of the larger and better-known ISPs provide appallingly bad service. Get a recommendation as to a good ISP from someone who has experienced good service.
You may need to sign up for a year's contract with an ISP. It might cost from £50 a year or more.
Your ISP will tell you how to set up your web site. Basically, you need to upload the web site software to the web server (a computer run by the ISP) that you will be using. To upload the software, you will need to use FTP - which is an Internet communication method for uploading to a server. (FTP = File Transfer Protocol.) See below.
You need to download the YourOwnSite software. You will then have a zip file on your computer.
You unzip the zip file using Winzip or a similar program. Unzip it into a folder such as /yourownsite or some other convenient place. If you don't have Winzip or similar on your computer, first obtain it via the Internet.
You will now have the YourOwnSite software in your /yourownsite folder or similar. Now you need to upload it to your web server (at your ISP). For this you use FTP. How to do this is explained under how to use FTP to upload and download files.
'Straight from the box', your new site will look rather like YourOwnSite itself. There is a lot you can do to tailor it: change the colour scheme; add more graphics; add pages and the menu; suppress pages. This is described in how to personalise your site.
There is a simpler way of achieving the above: by using the YourOwnSite service. If you use this, you will be using YourOwnSite as your ISP. Further, you have the option of using a sub-domain on the main YourOwnSite domain (for example: yourname.yourownsite.com instead of www.yourname.com), although you can have your own domain name if you wish. This ISP service is free for the first month and costs £50 a year thereafter. See how to do this here.