iTunes - Transfer vs. Sync vs. Backup
I have a new ipad2 and an iphone 4 running IO5. They are my first Apple products. I can figure out most things by hit and miss, but I obviously need iTunes for Dummies since I can't seem to get a handle on iTunes.
What exactly is the difference between transfer, sync and backup? Let's say I download an app to my phone. When I sync the phone in iTunes, doesn't this app automatically get copied (transferred?) into my library? And then I sync my ipad to iTunes, does this program now get copied to my ipad? And what is backup? Is that something I have to initiate? iTunes says my last backup was last night. I did not do it. If I delete an app on my phone, must I also delete it from my library? And if I don't, will it be copied back during the next sync. Is backup different from the items I see in my library?
Appreciate a simple explanation of the differences between syncing, saving and transferring and when to do each.