The information you fill includes,

• Billing contact - the name and address of the person or organization who will pay for the registration and subsequent renewal of the domain name.
• Administrative contact - the name and address of the person in charge of the domain name. This person is the one authorized to make the changes later to the information entered while registering.
• Technical contact - usually the name and address of the  administrator of the server where you host your site.
• DNS entries - Domain Name Server entries. These are the names or numbers of the servers where your site will be hosted. 
• Login and Password - for your domain name. This is extremely important and is different from the login and password you will get for your web site.

All of the above could be the same person or company.

Many will register your domain name for an unbelievably low price but will not provide you with a login and password or an interface for you to manage your domain name.

Once you register, allow 2-3 days to see your name in the whois database. The whois database is a directory of all the millions of domain names on the internet. To see your name in the database, select  the whois link on the registrars' web sites and follow the instructions.

The next step is to consider the costs and technologies for your site. Read the section on technologies for your site for more information.