Every website has a unique address - a domain name - for example yournewsite.co.uk.
Your business may already have a name, in which case you will wish to use this - or a version of this - as your domain name.
When choosing your domain name:
Check the availability of your chosen domain at 1&1 Domain Checker.
Enter a prospective domain name and tick the checkbox(es) for the appropriate top level (eg .co.uk) and then click the blue button "CHECK". Your chosen name will then be displayed along with a message - "available" or "already registered" - plus, a usually totally unsuitable, list of alternative suggestions!
The cost of domain registration is approximately £2.00-£3.00 (+ vat) per year (usually with a minimum 2 year registration period).
You can register your domain name at the same time as ordering your hosting package. See Hosting.