There are many applications for building a store/check out on your website. Also, a lot of people like to use websites like Smugmug as their on-line store.
Personally, I use something called
Photocart. Quite a few other photographers I know, use it as well. It's an application that you buy and load onto your website. I like that is resides right on my site, so I don't have to send customers to another site. It's very customizable and has a ton of features.
With something like this, the application takes care of the galleries, client info and handles the check out etc. but you still have to print the images and take care of shipping. Some of the website options will take care of printing and shipping for you, but they also take a commission from every sale. If you have the time to do it yourself, you can keep all the profits but if you are rather busy, paying the commission to outsource the printing & shipping might be a good idea.