A domain name such as siteseen.co.uk is divided into three parts. The top level is the .uk and is country specific or describes the site type i.e. com for commercial or org for organisation etc.
The second level refers to the site type such as .co for business and .ac for universities.
The third level is usually your business name e.g. siteseen.
N.B. Did you know that all Internet addresses read from right to left!