App plugins are a new kind of grafana plugin that can bundle data source and panel plugins within one package. It also enable the plugin author to create custom pages within grafana. The custom pages enable the plugin author to include things like documentation, sign up forms or controlling other services using HTTP requests.
An App is a bundle of panels, dashboards and/or data source(s). There is nothing different about developing panels and data sources for an app.
Apps have to be enabled in Grafana and should import any included dashboards when the user enables it. A ConfigCtrl class should be created and the dashboards imported in the postUpdate hook. See example below: