How to transfer apps to my Mac

Hi folks,

I tried to transfer iPod apps to my Macintosh, to be able to have them ready to transfer to my iPhone. But there was a problem.
A message "this computer is not authorized to ..." "Click store, then authorize this computer". Where is this selection???

Thanks in advance
Spiros.

In the iTunes menu bar.

Click on "Store", and then authorise this computer...