How a website is better than an newspaper or magazine ad or brochure.
Customers often hesitate to call or stop by a business they're unfamiliar with because they do not know who or what to expect. A website can eliminate that initital-contact anxiety because a website surfer doesn't have to worry about looking stupid in an unfamiliar situation.
Hence websites are a very low cost way of presenting your business to interested customers. On a website you can present an amount of information which would be prohibitively expensive any other way.