As best as I can understand, iBooks are much just like interactive PDFs. What language are they saved in, and what would be a good solution if I want to display or use an iBook in my app, which is written in Objective-C?
Here's a good guide that breaks down the basics of the iBooks concept and how they work and can be produced:
http://mattgemmell.com/2012/01/19/ibooks-author-for-authors/
As for the points you have raised:
Well, the iBooks format is a zip-like archive of assets. There's no language there per se, but the iBooks Author Mac app assembles your project and associated files into the required format.
Not possible. You can display normal documents that iOS supports like PowerPoint, Word, PDFs etc through a QLPreviewController
or UIDocumentInteractionController
for example.
I'd definitely recommend downloading the free iBooks Author
Mac app from the Mac App Store, linked below:
http://itunes.apple.com/gb/app/ibooks-author/id490152466?mt=12