Do online stores write without CMS and sales modules?

Question

CMS

Good day!
A few days ago, I asked questions about the engine for an online store
and how to connect it.
Having chosen OpenCart, I could not install it and connect it to my template, I did not find understandable manuals in Russian.
I want to try to write my own module for working with a shopping cart, placing an order, registering and adding content, but I don’t know how to do it correctly with a minimum number of problems.
I don’t understand the principle of the basket, its database structure and how it is tied up with orders. I don’t understand how to make adding products to the cart work even for unauthorized users?
How difficult is it to write it yourself so as not to use third-party modules?
Explain, please.

Answer 1

Try these life articles

Answer 2

It's not difficult, but judging by the fact that you couldn't even install and configure someone else's product, it's easier for you to hire a programmer.

Answer 3

Link the cart to the user's session. When authenticating, move the cart to a new session.
The complexity depends only on your skills and knowledge of the CMS / framework that you will use as a basis, or an understanding of the application architecture as a whole if you write from scratch yourself.