There is no way to save things to the Newsstand. Newsstand is a folder/app that displays other participating magazine apps. You have no control over what shows up there, other than to buy a magazine that uses Newsstand.
The easiest way to find those apps is to browse the Newsstand category in the App Store. Also, any app that uses Newsstand should state so, and will (usually) outline it's subscription model in the Apps description. The apps are generally free, but the magazines (purchased in the app) are normally paid for. You do (again usually) get one free magazine as a sample.