Thanks to extensive practice with whips, you gain the following benefits:

• Whips deals 1d6 points of damage instead of 1d4.
• The Whip's reach increase, by 5 feet.
• When you use an attack action, you can forgo an attack and to attempt to make a large or smaller creature become grappled and prone with your whip, if they fail a STR or DEX saving throw (the creature choose which type of save it is). The DC equals 8 + proficiency bonus + Charisma modifier. If the creature fails the saving throw, and becomes grappled as well as prone, you must keep hold of the whip in at least one of your hands to maintain the effects. The whip also cannot be used when holding a creature in this way. The creature can use its action to try and escape the whip's hold. 
• When you take an attack of opportunity, you can forgo the attack with the whip and attempt to make a large or smaller creature become grappled and prone with your whip, if they fail a STR or DEX saving throw (the creature choose which type of save it is). The DC equals 8 + proficiency bonus + Charisma modifier. If the creature fails the saving throw, and becomes grappled as well as prone, you must keep hold of the whip in at least one of your hands to maintain the effects. The whip also cannot be used when holding a creature in this way. The creature can use its action to try and escape the whip's hold. 
• When a large or smaller creature is grappled by your whip, you can pull them towards you as a bonus action, at the DM's discretion, up to 10 feet. Your strength score should be taken into account and an athletics check, might have to be made. 

If you are not playing an Hexblade Warlock there is a variant version of this feat call Whip Expert.

If you are playing a Battle Smith Artificer there is a variant version of this feat called Whip Expert (Battle Smith variant).