How to render products on a collection page from my database using Theme App Extensions?

[DevBijan]

Hi all, I am building an app that let's merchants organize products in a specific way, and allows customers to select their specific option. Once a customer selects their options I want to render a collection page with the products that apply to the customer's selection.

The products are organized in my database, and I am trying to use url query parameters to filter out the collection page.

What I am having a hard time understanding is how can I effect an already existing collection template, or create my own page so that there is a collection page that fetches info from my data base and renders out the correct products.

Any help is appreciated, thanks!