How to create a buy button?

Question

CMS

Hello.
The level of my knowledge in WP 0/10
I've been trying to solve this issue for a couple of days now. Maybe everything lies on the surface)
In the demo template store (www.site.com/?product) there is a "Buy" button and the ability to select the quantity of goods.
The task is to transfer to a specific page (not in /? product ) the function of choosing the quantity of the purchased product and the "Buy" button.
Through the shortcode, I could only add the "Buy" button, but it turned out to be a stupid button like "[add_to_cart id="" sku=""]", that is, it sent as many goods as it is written in the short code, but this does not work , because Each order is a different quantity of goods.
Thank you all in advance.