When you follow a training plan, the system will automatically try to connect each activity that you add or sync to the correct workout in your training plan.
The system does this by looking at the date of the activity (one calendar day before or after the scheduled date is allowed), the workout distance (a certain difference in distance is allowed), and duration (again, a certain difference is allowed).
When the system has linked an activity with a workout, this workout will be marked as completed in your progress view. Once you have completed all workouts in a week, the entire week will be marked as completed.
If, for any reason, the system couldn't connect an activity with a workout it's easy to do so manually:
Use the Link option to connect a workout with an existing activity you have already added or synced to your profile. Use the Add option to quickly create a manual entry for the workout. The system will prefill the date, distance, and duration with the defaults from the workout.
If, for any reason, a workout is incorrectly marked as completed you can click Unlink to allow you to select another activity, or add a new one.