More accurately, AoA is the difference between the chord line and the relative airflow. The Chord Line is a straight line from the frontmost part of the wing ie the bit that first comes in contact with the airflow - the leading edge - to the rearmost part (erm...the bit that last sees the airflow, the trailing edge).
Imagine a thin plank moving through the air or, better yet, find thin plank and hold it horizontally while you spin around (or even hold it out the window while driving but best get someone to help). If the plank was held so that the leading edge was at the same height as the trailing edge as it moved horizontally through the airflow the plank would have 0 deg AoA. If it was rotated 90 deg so that the front edge was directly above the rear edge then the plank would have a 90 deg AoA. Each degree that the plank is rotated to raise the leading edge above the trailing edge increases the AoA likewise.
Angle of Attack is always measured against where the airflow is coming from, not the Earth's surface. That same plank could be moving vertically and still have zero, 90 or some value in between for its AoA, depending on how you oriented it.
For a flate surface (ie not cambered or wing shaped) zero lift is produced at 0 deg AoA, increasing as the AoA is increased to some amount and thereafter reducing until at 90 deg there is no lift being produced.