From what I've seen so far it seems that AIR is like a shell to run FLASH in.
This is generally true. However, AIR adds a significant number of features for creating independent, non-browser, cross-platform applications. For example, in AIR you can create new windows, read and write files, access a SQL database, display HTML, and much more.
The core of your presentation/application will probably involve the same Flash features that you would use in the browser, so learning Flash would probably be the best starting point.
http://www.adobe.com/devnet/flash/ has information and tutorials for learning Flash.
Note that if you can do everything you need to in Flash, and you don't need any of the AIR-specific features, you can also create a Flash projector file. These have an advantage that they don't need to be installed, the viewer can just double-click.
Thanks for response. I wonder if actionscript will change in CS5?
There will be new APIs to use, but the language itself will not change.