What is Orb Walking and how to Orb Walking

1) Only use manual casting of arrow effects (hence, the "orb.")

2) You'll note that after manual casting the attack, the projectile leaves the hero rather fast and he then stands around looking stupid (Harby jiggles sometimes, Viper flaps his wings, etc.)

3) The above is known as backswing; if you don't cancel it, a running hero stands a good chance at getting away. If you DO cancel the leftover animation, you can chase extremely effectively.

4) Orb walking does NOT increase DPS - it is only a way to chase and not draw creep aggro at the same time. Once you get a few IAS items, better to just autocast.

Orb walking is manually casting an arrow, then animation cancelling to negate the backswing time.