how to transfer media from go pro to iMovie Mac

The transfer method may vary with the particular model of GoPro. You should look at your GoPro user manual for instructions. Here's the link to the GoPro help menu where you can navigate to your GoPro Model and then the User Manual. if you have misplaced yours.

https://gopro.com/help/productmanuals

For example, Page 56 of the GoPro Hero3 Black Edition user manual has the following instructions for transferring files to a Mac:

-- Rich

Once you get the files on your desktop you can drag them into an iMovie project time line or use the iMovie import window to import the files.

-- Rich