Within SPScriptlet 2 I'll show how to use SharePoint 2013's REST API to query common SPI properties. In the following example I've built a SharePoint App using Napa, first of all it's important that your App has "Read" permissions on "Web" in order to ask for the web's title. If you aren't yet familiar with the concepts of App- and Host-Web, you should first dig into these topics on MSDN (http://msdn.microsoft.com/en-us/library/fp179925.aspx).
Consider your app has the following HTML
If you're looking for the source, check my public github repository at https://github.com/ThorstenHans/SPScriptlets