What it measures
Face Angle tells you which way the clubface is aimed, left or right, at the instant the ball is most compressed. It is measured at the actual contact point on the face, in degrees relative to the target line. Because of that, the curved face of a driver matters: a strike near the toe reads more open and a strike near the heel reads more closed, even with the same swing. It is about horizontal aim only; the up and down tilt of the face is Dynamic Loft.
For a right-handed golfer, a positive number means the face points right of the target (open) and a negative number means it points left (closed). Zero means the face is square to the target line. Note that this is relative to the target, not to the path the club is swinging on.
Typical numbers
There is no tour average for face angle, since players aim to start balls both left and right. Good players typically keep the face within a degree or two of where they intend to start the ball, and that small spread is a big part of why their dispersion is tight.
Everyday golfers often see the face range several degrees either way from shot to shot. Even small numbers matter: with a driver, every degree of face angle moves the start line by close to a degree, which is roughly 4 yards of start direction at 250 yards before any curve is added.
What changes it
Grip is the first lever. A stronger grip (hands turned away from the target) tends to close the face; a weaker grip tends to open it. Wrist position at the top of the backswing, the amount of forearm rotation through impact, and how the hands are positioned at impact all change it.
Setup counts as well. Many golfers aim the face off target at address without knowing it. Ball position matters because a ball played forward is met later, when the face has usually closed more, and a ball played back is met earlier, when it is still more open. With the driver, impact location on the bulged face changes the reading as described above.
What it changes
Face Angle is the main driver of Launch Direction. The face accounts for about 85 percent of start direction with a driver and about 75 percent with an iron; club path supplies the rest. It also sets half of Face to Path, so it directly affects Spin Axis and curve.
Face Angle has a smaller link to height and spin as well, because an open face often comes with more loft added and a closed face with loft taken away.
How to use it
If shots start in the wrong direction, look at the face first. Do not aim for zero by default; aim for a face that matches the shot you want, a little right of target for a draw and a little left for a fade, relative to your path.
Bay drill: pick a target on the screen and set two tees a club length in front of the ball to make a gate on your start line. Hit five shots trying to start the ball through the gate, then five trying to start it just left, then just right. Watch how much Face Angle had to change for each, and note which grip and setup made the face behave most reliably.