[Vuejs]-What exactly is programming on the server side in web programming

Stuff like parsing CSV files is often on the server side (for example, in your Node.js server code), but it can easily be done in the browser on the client-side, using just a static HTML page and JavaScript file. See https://stackoverflow.com/a/26298948 for how to read and parse a file in JavaScript purely in the browser.

the server-side is where is written the business logic of your application core with some language such as Java, PHP, GO, among others. The client-side is the layout of your application. Hence, this kind of process such as parse a .csv file, database interactions, generate PDF files, Authentication, etc.

I suggest learning how to build a REST API and AJAX to consume your API from your client side.

Here is a link to learn about APIs: Introduction to web APIs – Developers Mozilla, there is another link about AJAX: Ajax – Developers Mozilla

Since you are new to web development, I first suggest you to learn 3-tier application architecture as all of the web applications are based on this architecture. Now once you learned the server side part of the architecture, you should start making small applications which uses server side and the database. Since you are already using Vue.js and hence javascript, you will feel more comfortable using Nodejs for server side programming.