Reading between the lines, I'm guessing you want information about iPods versus other MP3 players that are on the market and are not asking the question about what is the difference between and iPod portable music device and an MP3 music file.
Here's my answer from a previous Yahoo Answers:
For basic features of playing digital music, there's not much difference between an iPod and other MP3 players.
However, if you really want to load up that MP3 player cheaply, certain players with PlaysForSure have a distinct advantage and long term cost savings over the iPod.
For $10 a month, you can fill up a 5GB player with over 1000 songs or a 30GB player with almost 15,000 songs. That's less than a penny a song a month! PlaysForSure enables this kind of long term rental of music on players. You can download songs from Yahoo Music Unlimited To Go, Rhapsody To Go, or Napster To Go.
Apple iPods do not permit rental or subscription music. So you have to buy songs on CD and rip them yourself or puchase songs at 99cents a song from iTunes.
With a subscription service, you can still buy music too, but it is only 79cents a song.
And, lest you think the MP3 players aren't as cool as the iPod, Creative's players are easy to use, come in lots of colors, and, oh yeah, their Creative Zen Vision:M music and video player won best of show at the 2006 Consumer Electronics Show (CEA) in Vegas in January.
I have a Creative Zen MicroPhoto. It's easy to use, carries lots of tunes, and has more storage for less money than a comparable iPod. And it works with subscription music services which was a key decision factor for me.
You can be hip and poor and buy an iPod, or you can be cool and have a few more bucks in your pocket with non-iPod MP3 player.