There's plenty of useful/helpful stuff out on the web. Background and general knowledge are always helpful; and the further you advance, the more understanding is expected instead of rote answers.
Anything concerning law or procedures will be different in other countries, but aerodynamics, engineering, etc is the same all over. (Careful with southern/northern hemisphere differences - you'll find them in met and nav occasionally.)
For most subjects (e.g. nav) there are no required/correct ways of doing things - you can use whatever method you like, if it gives appropriately accurate answers. So look around for methods and techniques that suit you.
The FAA handbooks are very useful, look through the "library" section of their web site - and lots of our stuff (e.g. engineering) is based on that. The NZ CAA has some good material on the web.