In reply to Sonya Mc:
Plug your Garmin in to your Mac with a USB cable.
Open Finder (blue/grey square with a smiley face in the Dock)
Find your GPX file and copy it.
In the left hand pane you will see the Garmin listed as a device.
Click on it then in the right hand pane double click the Garmin folder and then double click the "New Files" folder.
Paste the file in to this folder.
In the left hand pane click the up arrow icon next to "Garmin" to unmount the device.
Now reboot your Garmin
It should copy the GPX file in to the courses folder converting it to the internal FIT format.
BTW, GPX files don't store the turn hints/directions for that you need to convert the file to TCX format.