Off

• By turning off the auto-orientation, or auto-rotation, you are allowing your project's layer to move on its own. When off, the layer will not follow the motion path, which is the dots marking the position of each layer in a frame to denote the motion within the frame. Turning auto-orientation off is useful for judging how the frame is naturally orientated and which orientation option you want to use for it.
  
  

Along Path

• By selecting "Orient Along Path," you are allowing the auto-orientation to follow the motion path, or the motion within the frame itself, along the actual movement, rather than orientating it using a layer you made for adjustments on the frame. According to Adobe, this is most useful when you are working with the point of view of a driver looking at the road ahead.
  
  

Towards Camera

• This auto-orientation option is the opposite of Orient Along Path. When selecting "Orient Towards Camera," you are rotating the composition away from the motion path so it facing the "active camera" -- the first camera in the Timeline panel, which is also the default view camera. This option can only be used on 3D layers, and not with 2D layers or camera and light layers.
  
  

Towards Point of Interest

• When selecting "Orient Towards Point of Interest," you are rotating the composition so it is facing the point of interest. The point of interest is the place in the composition where the light is directed. When using this orientation option, you are directing the view towards the focal point, or the point where the eye is naturally drawn. This effect can only be used for camera and lights layers, as they are the only types with points of interest.