Primarily, your domain name is used for e-mail addresses and Web sites. Once you have registered your domain name you will be able to develop a Web site with the Internet address of http://www.yourco.com, or whatever other extension you registered. Your e-mail addresses will look like annoyance@yourco.com.You can also move any existing Web site onto your new address.
Your Web site address and e-mail address can be printed on your stationery along with your other contact information.
You can have a Web site or e-mail address without having your own domain name, but these generally look less professional.