Preparation

Install Node.js

See How to install Node.js?.

Note:
You need npx to run commands later. npx comes pre-installed with npm (Node Package Manager) starting from npm version 5.2.0. npm comes with Node.js, so you need to install it.

Pick an editor

Pick your favorite editor or use Visual Studio Code.

Learn React basics

If you're not familiar with JavaScript, you may try this tutorial: "Quick Introduction to JavaScript."

Learn HTML basics: Introduction to HTML

Learn CSS basics: Learn to style HTML using CSS

If you're not familiar with React, try to learn here: "Quick Start - React."

What is Pomodoro?

The Pomodoro Technique is a time management method developed by Francesco Cirillo in the late 1980s. It uses a kitchen timer to break work into intervals, typically 25 minutes in length, separated by short breaks. Each interval is known as a pomodoro, from the Italian word for tomato.

Photo from Wikipedia