What applications do i need to make a Newsstand app?
Newstand content is simply an iOS Application that makes use of the Newsstandkit, so you might start with Xcode and a one year membership to the iOS Developer Program.

When you enroll in the latter, you will learn what things can be discussed and asked about publicly and which parts of the program are covered by an Non-Disclosure Agreement (NDA).

You don't need the paid membership to download Xcode and start learning and crafting your first Newsstand app, but you do get access to many training videos, a discussion area where you can speak to other developers and Apple on NDA topics. The ability to sign and install apps you develop on some test devices to work on development before they are ready for sale on the App Store is also critical for proper QA.

There are also many other paid options to developer Newsstand apps, but I would start with free and training like the dedicated page for developers to learn Newstand:


https://developer.apple.com/newsstand/