You can access the logbook by swiping down or pressing the upper button until you see the logbook icon..
Tap on the log entry you want to view and scroll through the log by swiping up or down or by pressing the upper right or lower right buttons.
The log entry remains gray until it has been synced with your online account.
To exit the log, swipe right or keep the middle button pressed. You can also just double-tap on the screen to return to the watch face.