Ciri's Story: The King of the Wolves - Velen
This quest begins immediately following completion of the Bloody Baron story quest. In the Witcher 3, this is the first quest that you're controlling Ciri. I recommend that you pick up all Alchemy Ingredients that you come across as they're used in this quest as well as carry over to future times when you're playing as Ciri.
When you begin you'll want to follow the river bed until you run into Gretka (pictured above). She is under attack by a few wolves and will join you once you save her. Follow her for the next part of the quest until you stumble into a body strewn about on what looks to be half a boat. Much like with Geralt, Ciri will stop to investigate what killed the man.
During this scene it is most important that you select Chest, Legs and Belly as this will lead Ciri to conclude a werewolf killed the man. If you do this part wrong then Ciri will conclude something else killed him and incorrectly prepare for the upcoming fight making it more difficult.
Collect the required Alchemy Ingredients then there will be another cutscene where Ciri crafts the oil you need. When that's finished follow Gretka into the cave where you'll conclude this quest with a battle against the King of Wolves, the werewolf. As aforementioned, if you incorrectly prepared the fight will be a little bit harder, not only will your blade deal less damage to it but the werewolf will also use a buff increase its size and damage done.
After defeating the werewolf there will be a cutscene followed by you gaining control of Geralt again. You'll be thrown into the next story quest by the name of Family Matters. In addition to this quest you'll also receive the Ciri's Room side quest, which you can complete now.