1. Spread it on the garden and flower beds.
2. Enough to barely cover the area.
3. Only if there are still hot coals.

Likewise.

Be careful with woodashes that you do not spread them on plants that like acid soil or in areas where you are going to plant acid loving veggies, such as potatoes, radishes, watermelons, and watch out too for azaleas, hydrangeas and blueberries and strawberries, all acid lovers. Corn, beans cants all the brassicas can stand a sprinkling. And lilacs, iris and daylilies can also tolerate ash. In fact bloom better with a little. We sprinkle ash around our pie cherry tree which sweetens the cherries up. And the asparagus gets a lot. We burn with wood but never have enough ash to go around.

Woodash has a pH of 10 so don't go overboard using it especially on acid loving plants.