You are proficient with a whip.  You've learned how and when to use it and when it is better to use it as a tool instead of a weapon.

• You may make a Dexterity (Sleight of Hand) check to secure your whip around an object or grapple a Medium or smaller creature.  
• While your target is grappled in this fashion, you may make a one-handed melee attack with a light weapon without proficiency.

Escaping a Grapple. A grappled creature can use its action to escape. To do so, it must succeed on a Strength (Athletics) or Dexterity (Acrobatics) check contested by your Dexterity (Sleight of Hand) check.

Moving a Grappled Creature. When you move, you can drag the grappled creature with you, but your speed is halved, unless the creature is two or more sizes smaller than you.