Use npm scripts to run or build solution.
npm install
npm start
npm run build
In all above mentioned cases, you can use yarn instead of npm.
If you cannot install dependencies or run project, due to issues with building node-sass - be kind to install build tools for your operating system. Also, be sure to use Node v12+. Reinstall of Node.js can help you.
# Windows: run from PowerShell with administrative rights
npm install --global windows-build-tools