the ones you do not want, will not be transferred from your iPod to your computer when you plug the iPod in.
By default, the iPod does not transfer tracks from itself into iTunes. To do that, you would need the iRip app that is mentioned below.
In your case, just connect the iPod to your computer, sort out what tracks in iTunes you want to copy to your iPod and hit the sync button.
Any tracks that are on the iPod but not on the computer, will be erased from the iPod; leaving you with just the tracks that you wanted
I have a new Ipod with songs i dont want. i want to import the ones from my computer to my ipod but not from my ipod to my computer.