On your new mac install iTunes and just enter the info from your account and then it will be on the mac. Then authorize the mac.
As far as moving from pc to mac goggle is you friend. Here is just one ling that will walk you thru it faster then I can type it.
How to move your iTunes music library from a PC to a Mac without losing metadata (ratings, play counts, album art, etc.) » JakeBouma.com
Hope this helps
Clay