This question seems to be asked a lot by small businesses who are getting a new (or possibly their first) website. And really, a lot of times "Drupal" is replaced with "WordPress" or "Joomla!" or something else in that sentence. I'm not going to get into a comparison in this post — that's for later!
Sometimes, what they are trying to verify is if their clients and/or vendors can have a secure area that they can log into for things such as project management. Or they are wanting to know if they can sell products through their website. Or they are wanting to manage a mailing list through their website. The list can go on and on. (Even politicians ask if they can track records and manage relationships with constituents and donors.)
The answer to all of the above is a resounding YES. Drupal and do all of that and more. Drupal is a framework to build a website upon. Pretty much if you need your website to do something, Drupal is flexible enough to make it easy. Unless you are planning a website that will never change in the future, Drupal is perfect for your small business.
Feel free to drop me an email via the contact page to discuss what I can make Drupal do for your small business!