When using Navigate to follow along your route, you have several ways to control your map view and orientation. When you first open Navigate, your location will be centered on the map and North will be up (↑ top of phone). Once you press 'Start', however, the orientation will adjust to face your direction of travel and the map will be slightly tilted to give you a preview of what's ahead. When using this mode, you'll notice that if you move your phone around, the map will adjust directions to keep your direction of travel pointing upward.
You can adjust your orientation by tapping the red and gray compass icon — this will adjust your view so that North is up, and will also switch to a bird's-eye view of the map (no tilting). Tapping the compass icon once again will switch you back to the original mode of following your direction of travel.
If you zoom in or out on the map, or pan away from your current location, you'll notice the 'Re-center' button will appear at the bottom left corner. Tapping this will center your location on the map, and will return your orientation to follow your direction of travel with the slight tilt.