A web site is like your giant public bulletin board where people can get information on how to find you, where you are located, what you have to offer, why your service is unique, and what's new in your company. It also is easily updated and changed frequently, and is a communication forum through which your customers can communicate back to you with questions, concerns and feedback on their needs.
I tell clients that getting a website is like getting a telephone. They both have similar cost structures. The website cost is like the cost of the phone and installation. You pay one time and the equipment is yours. The hosting cost is similar to your monthly phone bill — you own the equipment but you pay for the service of being able to use it. The domain name registry is like the phone number — a unique way to get in touch with only you.