Domain Name Extensions are 1 of the 3 parts that make a up a domain name (a domain name is what is commonly referred to as a website address, like bbc.co.uk or bemoreonline.co.uk)

The three parts of a domain name are shown below and they are all equally important ie you must type them correctly in to a browser (like Internet Explorer) to get to the right website;

As an example mywonderfulnewwebsite.com and mywonderfulnewwebsite.net could be two completely different sites.