Newly created planning tracks are created in the centre of the current plot. So, start off by navigating to the part of the world where you roughly want your vessel tracks to be. You'll make more detailed changes to the track location once the track is created.
Next, you must select "Create Track Segment" from Debrief's Drawing Toolbar, or the menu.
Next you'll be invited to select which parent track to add the track segment to. In this instance, we don't have an existing track, so select "[New Track...]" from the dialog. Clearly if you were extending an existing planning track you'd select it.
Since we're creating a new track we now see a couple of dialogs associated with the new track. First we must give the new track a name:
Next we must specify the starting date/time for the track:
Once we've finished specifying the track, we must specify a name for this particular leg of the track:
Your track will now appear on the screen, and also in the layer manager.
Once you've created a parent track, next time you can select it from the first dialog - after which you just need to specify a leg name,