How do I upload a new movie onto my iPhone without having to sync it with iTunes?

Question

I am new to iPhone and all this syncing is so frustrating and time wasting!
I am using iTunes on the same computer and every time I want to upload a new movie, video or anything else, iTunes keeps telling me that I am changing libraries and that it will completely wipe out everything from my iPhone. why does this happen? how many libraries are on my iTunes? I am using the same apple id on the same computer and it still wants to delete everything from my iPhone? Is there a different library for EVERYTHING on my phone?

Answer 1

as I explicitly wrote in my first post:
of course my iPhone is already synced to the same computer!
I wanted to add a movie on my iPhone today on the same computer and through the same iTunes that I already synced my iPhone with and when I wanted to upload the movie onto the phone it told me that I am now using a different library and that everything on my phone will be deleted. I also tried to do it manually because I don't want to waste time by backing up the phone, erasing everything from it and then putting it back onto the phone, and iTunes told me the same thing: that I am using a different library etc etc.
the other day I wanted to put a new ringtone on my iPhone and iTunes did exactly the same thing!
how can I be using a different library on the SAME COMPUTER and on the SAME iTunes for different things that I want to put on my iphone?
another thing:
if using iTunes indeed were as simple and as easy as you say it is, then there wouldn't be as many complaints about it as there are. also: calling someone ignorant just because they don't want to be bothered by the restrictions, complications and unfriendliness of iTunes is pretty lame!