NPM : You must have to npm install packages. You can do this by running npm install from the root of your project to install all the necessary dependencies :
$ npm install
Run npm run dev for a dev server. Navigate to [http://localhost:3000] . The app will automatically reload if you change any of the source files.
$ npm run dev
$ npm run generate
$ npm run build
$ npm run start
For detailed explanation on how things work, check out Nuxt.js docs.