I am new to SharePoint. Currently, I am trying to add this app (https://github.com/SharePoint/sp-dev-fx-webparts/tree/master/samples/react-script-editor-onprem) to my SharePoint site. I have followed the instructions given, but it does not show on my page after installing the app.
Secondly,after it finishes installing,you could see it in your site contents. Thirdly,we need to add the web part to page and add script in it.If you do not host your web part in CDN,you still need to run a command ‘gulp serve --nobrowser’. And you could know more about how to deploy SPFX from here: https://docs.microsoft.com/en-us/sharepoint/dev/spfx/web-parts/get-started/build-a-hello-world-web-part