Hi Jessica. I have an N73 and often transfer pictures from it to my Mac.
I usually start, from the main screen, by pressing the middle button on the right edge of the phone to bring up the picture gallery. When I have found the one I want to transfer I select the envelope icon in the group of five icons on the screen and "click" it. A menu of transfer options comes up, with via Bluetooth halfway down. Selecting it brings up a devices list - if it is initially empty it will be searching for your Mac - and I scroll to my Mac and press the button beside Select.
On the Mac a widow pops up which tells me that the N73 is sending a file; I have to click Accept for the transfer to happen.
At what stage does your experience differ?

AK