That large shape describes the boundaries of the brow ridge on top, the edge of eye socket where it marries up to the zygomatic process on the lateral side, and the bulge of the eyeball and skin folds on the bottom, and then on the medial side where the eye socket meets the nose bridge bone (note: not the tear duct!). It's a construction technique used to wrangle the complex shapes of the eye into a simple, attractive shape first, in which the smaller secondary and tertiary forms can be drawn. It's a good example of working big to small to create accurate proportions and achieve the primary big effect first, then build upon that by adding smaller forms and details. Yes, the eyeball, lids and eyelashes are secondary, not primary forms when you're dealing with the entire head - features in general. Going in right away to draw the eyeball and lids without this construction will probably result in wonky proportions and much more difficult circumstances for applying shading and lighting the entire eye. I think with experience you can relegate that construction phase to your mind and go right for the eye while keeping the larger shape in mind.