If it is already an mp3 file, you just drag it into iTunes from the folder it is in.
no, you don't need an account.
Normally, your computer will ask you if you want iTunes to be your default player before actually downloading the program. If iTunes is already downloaded, then I can't answer.
That happens when you aren't connected to the internet.
You can download something you've already downloaded again.
Two iPods will work with iTunes on the same account, so there shouldn't be a problem.
Albums bought from iTunes are downloaded from the iTunes store. You can burn the downloaded album on to a disc on your computer.
If not already installed on the computer the iTunes software can be downloaded from the Apple web site (See links below) and there is extensive guides to using the software too.
Open itunes. If you are connected to the internet itunes will automatically connect to the itunes store.
the only way itunes redownloads are free is if you downloaded (say a song) from itunes and you received a receipt for it and ffor some reason you accidently deleted it. Then itunes will allow you to redownload it for free because on your itunes account it shows you have already paid for the song.
If the applications are downloaded via iTunes, they will be automatically transfered to the iPhone during synchronization. Otherwise, the apps downloaded via iPhone will be copied and backed up to the iTunes during synchronization. So to transfer the apps to the iPhone, just connect the phone to the iTunes and sync. Click on iphone on the side bar, then apps up the top, then sync apps.
iTunes can be downloaded from Apple's iTunes page. (See links below)