Node allows you to run your typescript code (once compiled into javascript) outside of the browser. When you install NodeJS, it will come with NPM, a package manager to install other engineers' code.
NodeJS will let you run a local server so that you can access the web app you are building on your machine without having to update a server somewhere else. By doing so you can instantly see the changes you make.
Once you have Node installed you can run
npx create-next-app@latest --typescript
in your terminal, and then run
npm run dev
This will create a starter Next (React) app and start up a local development server to host it that you can access via your browser by navigating to http://localhost:3000