What is 'countersteering' and how is it used to initiate a turn on a motorcycle at speeds above 15–20 km/h?

1. Push forward on the left handlebar to lean and turn left; push forward on the right handlebar to lean and turn right
2. Pull backward on the left handlebar to turn left
3. Turn the handlebars completely sideways while keeping the bike vertical
4. Lean your body to the right while steering hard to the left