fwiw,
in a pinch, you can remedy the situation (likely, at least) by doing the following:
Leave the car in gear, stand outside your driver's door with the door open (as if you just got out of the car) and push on the a pillar/door jamb to rock to car forward and backward. The goal is to push the car as far forward and back as you can. It will "stop" when it gets as far as the teeth in the gear will let you roll, then quickly pull back until it hits the "reverse" (bottoms out in the gear and won't roll backwards.
Push back and forth, stop-to-stop 4 or 5 times and then retry starting. This action engages the teeth together tighter to get past a worn ring gear, or worn starter wheel. It just meshes the teeth closer together. This is not a permanent fix, nor will it CONTINUE to work.. eventually, the worn teeth may shear off completely, etc, so don't rely on this. Just as an "in case" you get stuck before you replace the starter.