Setting up a shopping platform is quite complex. In this post, I'd like to give you an idea of how this works.
Any webhost needs hosting, it's place on the web. I'm using Amazon Web Services, where I run my Linux machines. On top of that, I'm using a MySQL database to store all your data in, and PHP is our programming language of choice.
PHP offers basically all the functionally you could ask for, but to structure my programming and avoid reinventing the wheel, I use the CakePHP framework. It gives me all the functionality and precooked code I need, yet gives me enough flexibility to build what I want.
Finally we're storing all files on Amazon S3, basically the worlds biggest USB stick;-). It stores all the images and static files.
To make sure your shop is safe even when disaster strikes, we're making automated backups that are stored in a physically different environment. When our servers (based in Ireland) go down, we have backup systems ready in the US (Virginia), that can start working in 2 minutes. Your website will be online, even when a meteorite strikes the earth;-).