Building Price Comparison Website what do i need Exactly ?!

APIs and Databases are programming language independent. You can consume an API and interact with a database in any language that's been mentioned: JavaScript, Python, C, C++, C#, PHP, etc.

You're really asking about Web Application Architecture, which might be easier to understand once you've finished the current HTML/CSS/JavaScript stuff you're doing on Treehouse.

Once you've got the hang of HTML/CSS/JS you can start a project with something like a simple web server connected to a DB, and a front end page to display content and handle user input.

To get at your question of what you do and don't need: I would try to do something really simple (like setup Node.js and a DB on AWS free tier and build enough to get a simple input form working) because trying to dive into web application architecture before getting some context for it is probably going to raise more questions than it answers.

Once you've got that little bit of experience maybe research things like "Web Application Architecture" and "MVC". Understanding the MVC concept and having built something that displays a webpage that can manipulate a database table based on user input will give you a lot of context.

For your pricegrabber-like you could spin up a Linux VM, run Node.js, install and configure Postgres, throw Express on top of Node and write your front end in React. That's a popular combination. You could also run a (somewhat antiquated) LAMP stack (Linux Apache MySQL PHP) with a JavaScript front end and achieve a similar result. You could run httpd on Solaris and extend it with custom C modules. You could write a python script that grabs data from APIs and shoves it into a headless CMS that a Vue app reads from. The possibilities are endless but there's no point getting deep into the detail right now.

When you started learning C I'll bet you started with simple branching logic and console I/O, not implementing binary trees or even dynamically sized arrays.