It'll be something like this.........
Assuming that both Garmin & Radio are powered from same battery ( common ground ), the blue cable from the Garmin( Pin 3 ) connects straight to pin1 ( the brown cable ) on your radio .
You must also set the communications on your Garmin to be using ( transmitting ) on Port 1 .
If this is not correct , I am sure someone will be along in a minute to ammend .
The hardest part may be entering your MMSI on the radio , if you haven't already done it..........
Always try the search function for these sort of questions as many of us have had to seek advice ourselves .