Can you explain Warwicks W attack to me?

https://m.youtube.com/watch?v=Rro20bR4jnQ

Use his W to chase people down as if they were at low health. That's pretty much it, you just run really fast. It will let you ult a lot further for higher health people because of the extra movement speed, but it does nothing for you when chasing someone with a blood trail.

It passively gives increased attack speed to Champions under half health, while also giving increased movement speed towards them if you follow the path made out of blood. If they end up near death, the bonus triples, which is pretty significant. It has synergy with Warwick's passive that allows him to do bonus magic damage on hit, as well as heal off said bonus damage.

The active part puts the blood hunt mark thing on the nearest enemy within a certain range, so you can use it to scare nearby players, see if someone is in range of it, or speed up towards a target you're ganking.

When fighting an enemy below 50% health, Warwick gains extra attack speed. It's a lot of attack speed and combined with his passive and on-hit items like Titanic Hydra, this makes him very effective in a full brawl with another champion, as well as increasing his clear speed against big jungle targets like buffs and Gromp. The attack speed boost is further increased when the enemy is below 20% health.

When an enemy champion falls below 50% health, Warwick also begins tracking their scent. He gains movement speed towards those champions and can also see blood trails following their movement even when they're out of vision. This makes Warwick very effective at cleaning up kills after fights.

Warwick can also start tracking the nearest enemy champion by casting W. This triggers a blood hunt on the nearest enemy champion as if they were under half health regardless of their actual health total. Unlike Rengar's ult, it stays on that specific champion even if a different champion ends up closer to you later. It also only triggers the movement speed and blood trails, NOT the attack speed bonus.