git clone https://github.com/ionic-team/ionic-framework.git
cd ionic-framework
cd core
npm install
Notice that @ionic/core lives in core.
Make sure you are inside the core directory.
npm start
With the start command, Ionic components will be built with Stencil, changes to source files are watched, a local http server will startup, and http://localhost:3333/ will open in a browser.
Navigate to http://localhost:3333/src/components/. Each component has small e2e apps found in the test directory, for example: http://localhost:3333/src/components/button/test/basic
As changes are made in an editor to source files, the e2e app will live-reload.