Having your training data sorted in multiple places can provide many benefits. As I use Training Peaks I get all my athletes to load up their training data into Training Peaks so I can easily view the detail and provide comment on it for them.
Select from the two options:
Choose Connect and Sync if you have workouts data already stored on Garmin Connect that want transferred across to Training Peaks.
Choose Connect My Accounts if you are new to using Garmin Connect and don’t have any workout data stored in there to transfer to Garmin Connect.
Checkout this video on how to connect them.