if i sync photos from iphone to my mac fir the first time what happens

The transfer of photos from an iPhone to a Mac is an import. It is very similar to what happens when you move photos from any camera to the Mac (if you have ever done that). Instructions: http://support.apple.com/kb/HT4083

The iTunes sync can move photos the other direction (Mac to iPhone). That "sync" works the same way each time you do it -- it sets the non-Camera Roll photos on the phone to match the current iTunes photo page settings. Instructions for that: http://support.apple.com/kb/HT4236