You apps are actually saved in you itunes account. What I mean is that even if you delete every app on your phone, you can go to the app store and click on purchased and download them all again for free as long as you use the same apple id. If you have synced it in itunes they are also already there. My phone backs up to icloud but also syncs with itunes over wifi when it is plugged into a charger.
You can also just buy an app once and download it to multiple devices, iphone, ipad, itouch....... and only pay for it once.
Now if you are asking how to save documents to icloud or spreadsheets, that is a little different.