AFAIK, the two versions are completely compatible with eachother. They are both applications for editing, although the OS X version may be a little more 'complete' (content that can be created on OS X may not be able to be created on iOS, however iOS will be able to view the content).
As far as the 'where to save it' question, I'll have to refer you to this link. I've yet to use any of the iWork applications firsthand, although it is in the budget for month after next
Keynote app for iOS can open, edit and save presentations and can import presentations created on your Mac as well as share your presentations back to your Mac.
The most common way to share files is via iTunes but files can also be shared via email (with some size limitations), Dropbox and other similar apps. Keynote on an iOS device can save and share files to iCloud with other iOS devices, but Keynote for OSX can't directly download these files (yet) - you need to log into iCloud to access the files even if you can "see" them in iCloud on your iOS device.
There are some key differences you should be aware of between the iOS and OSX versions of Keynote:
- not all animations, actions and builds created on a Mac are supported on iOS
- the iOS set of available fonts is limited and not expandable, at this point, so some fonts used on OSX will be replaced by iOS Keynote
- you may find timing of some actions a bit off and need tweaking
There is an article on best practices when using Keynote for iPad that is worth viewing:
Hope this answers your questions.
When you connect your iOS device to your Mac, you use iTunes to synch the two devices. One part of that synch is to transfer files that you have specified.
It is important to know that files on an iOS device are stored with the associated app so Keynote files get saved to Keynote on your iOS device - this is different than files saved on a Mac in the Finder - when you delete an app on an iOS device, all the files associated with it are also removed from the device.
In iTunes, when connected to your iOS device, there is a section for apps that shows all of the apps on your iOS device - scroll down and you will find a section for file transfer to the various apps that can receive files - files for Keynote are placed in the Keynote section and the devices are synched. On the iOS device, in Keynote, when you tap on NEW, there is an option to open files from iTunes. You tap that option and Keynote imports and formats the file for use in Keynote on the device.
A better explaination can be found here:
With the new Keynote released for iOS and OS X the last few days, there is the promise in the "What's new" that files edited on one device will automatically change on the other devices if you signed in to iCloud on all of them.
I can confirm that this is not true for Mac as there seems to be no connection to iCloud from Mac Keynote at all. Or at least I couldn't find it. And there really is nothing in the Mac Keynote documentation about iCloud.
Someone at Apple made a huge mistake?
Oh let me get this straight about the Mac version, here is the update note straight from the app store. I don't think I misinterpreted the iCloud message right?
Ok I think I got it. Somehow Mountain Lion is required to use these features. I'm on Lion. Now what is that about? What on earth could require an OS update in order to get a small feature? Ok, I think I got the message. This is just laughable.
I believe the iCloud connection occurs IF you have both: updated iWork apps (Keynote, Numbers & Pages) AND upgraded to OSX 10.8 (Mountain Lion) - if you are still using Lion or Snow Leopard, the iCloud connection continues to be as you say - you need to log into iCloud from OSX. With OSX 10.8, this is supposed to change to as cuurrently advertised.
I didn't try making an iCloud connected app for OS X Lion, but as iCloud already exists in Lion (I mean, Apple required us to upgrade to Lion in order to use iCloud!), I don't see why you couldn't make apps for Lion that works with iCloud. Oh don't forget iCloud works very well on old OSes like Windows 7 (with some free small patches, not a complete OS update), and maybe even earlier - which makes us able to assume that these requried updates are NOT beacuse of technical issues, but because of money issues. I think Apple are shooting themselves in the foot with this kind of thinking. I don't think they really need to be this penny-pinching at all seeing how succesful they've gotten.
I'll need to get Mountain Lion anyway for lots of other reasons.