If you don't already have it, you gain proficiency with the whip.

- You can use your reaction to make an opportunity attack with the whip when a creature enters your reach.

- If you hit with a whip, you can initiate a grapple.  You may use Dexterity instead of Strength to initiate.

- If a creature is grappled by your whip, you may use a bonus action to make a contested Strength check vs that creature.  If you win, the target falls prone, but is no longer grappled.

- You deal 1d6 slashing damage with a whip or 1d4 slashing damage with a basic whip. (I use the equipment stats I. Wraith Wright's Comprehensive Equipment Manual)