1, Install NodeJS on your system. https://nodejs.org/en/
If you have already installed, check the version by using this command node -v
The current supported LTS version of NodeJS for the SharePoint Framework is both 8.x and 10.x. Notice that 9.x or 11.x versions are currently not supported with SharePoint Framework development. Previous versions of NodeJs https://nodejs.org/en/download/releases/
2, Install Yeoman and gulp
npm install -g yo gulp
Yeoman provides common build tools, common boilerplate code.
3, Install Yeoman SharePoint generator
npm install -g @microsoft/generator-sharepoint
It helps to create a SharePoint client-side solution project with the right toolchain and project structure.
4, Trusting the self-signed developer certificate
The SharePoint Framework’s local webserver, used when testing your custom solutions from your development environment, uses HTTPS by default. This is implemented using a development self-signed SSL certificate. Self-signed SSL certificates are not trusted by your developer environment. You must first configure your development environment to trust the certificate.
5, Create ClientSide SPFx WebPart
Navigate to your project folder by cd folder