When your website is built right, by professionals, it should be able to do the following for you:
Help you stay in contact with your customers.
Support your marketing efforts.
Get your business found easily on search engines.
Increase your sales leads, conversions and revenues.
Help you provide 24/7 customer service.
Improve the image of your brand.
Increase your reach, making your goods and services available to a global market.
Increase your availability. You can continue to offer services and support long after you have closed your physical doors for the day.
And so much more.