Install Slim Jetpack either via the WordPress.org plugin directory or by uploading the files to your server
Go to Settings–>Slim Jetpack and activate the modules you need. Configure them if the ‘configure’ buttons appear. You need at least ‘activate_plugins’ capability to access the configuration page.
Click ‘toggle’ to show the ‘deactivate’ button and the infinite-scroll module is only for twenty-xxx series themes, you may extend it to support your own themes.