I am new to node.js and am confused as to how to get started.

Fair enough. Just to explain a little bit about stackoverflow: contributors will expect you to be specific with your questions. You will not get anyone to basically write your entire code.

I am briefly answering, as you wanted to know where to get started with your project.

For a project like yours, you need to learn Java Script DOM, the Document Object Model.

The key commands (properly called methods) to learn here, as a beginner, are:

document.getElementById()
document.querySelector()
document.querySelectorAll()
element.getAttribute
element.setAttribute
element.InnerHTML

Variations of these will allow you to manipulate any (node) element, field, text, values, styles aso. on your frontend / website, as well as read them and generate a list (nodeList) for saving to your backend.

For this I also recommend you to learn the basics on arrays, objects and loops in Java Script, or you will not be able to structure your data before and after transfer.

Lastly; you need to build a server on your backend. You could learn how to write this in vanilla (plain / native) Java Script, but most would (at least initially) instal a library like Express. There are some Express tutorials on YT, that could get you up to a running server in half an hour.

To round up the experience, you may want to be able to permanently store the data, which is transmitted to your backend. There are many databases around. A basic start for many is MySQL. It is a relational database, which means it works with structured tables, like your favorite spreadsheet.

Please feel free to post some followup questions, accompanied by some code that you tried, some errors you got etc.