Domain names are used as a replacement for IP addresses. People and organizations register domain names from any domain registrar. These are companies which maintain a large database containing all registered domain names and which IP addresses they are associated with. Domains can also be renewed once the registration period is over, or else they will expire and be available for others to register. It is very wise to look at a number of different domain registrars and compare their prices and the services they provide before registering a domain name.
Domain names can have one of many extensions, and new extensions are being added regularly.
An important thing to know when registering a domain name is that you will be asked to specify Administrative, Technical and Billing contacts for your domain name. You MUST make sure that you are the Administrative and Billing contact for your domain. The Administrative contact can easily make changes to your domains settings making it point to another website for example, or change the owner information. You may also make yourself the technical contact, although it is recommended that your hosting company put their information if possible. You also need to know about DNS settings.