how can i used Mac to find my i phone

If your iPhone is powered on, connected to internet, and the find my iPhone app was enabled previously, you can use Find my iPhone.... as long as no-one else has reset the iPhone to defaults.

Otherwise, you can use your Mac to google a map of the places you have previously been to and then go there to see if thats where you left it.

Assuming that you enabled Find My iPhone on the phone before it was lost, you can use that:

http://www.ilounge.com/index.php/articles/comments/using-find-my-iphone-from-a-p c-or-mac/

If you didn't enable that, or any other similar thing, there won't be any finding it this way.