It's really easy to buy things online. Just choose what you want, click on it, go through the checkout process and after few days you get your items delivered to you. And all you do is to click few times on a website or tap few times on specific mobile application.
What happens behind the scenes is more complicated than you might think. Professional e-commerce solutions usually contain more than 10 different server systems, each doing something different. Here is a simplified view of a typical e-commerce infrastructure: