Here are some introductory videos on PowerApps from early 2016. The user interface and the functionality have been enhanced quite a bit in the releases that followed. Watch these to get the high level concepts and hopefully I will get to write about the cool features in the coming weeks.
PowerApps 101 - create a new app
PowerApps 102 - create app from templates
PowerApps 103 - Create apps connecting to existing data sources
Happy app building 🙂