Dogs usually lick peoples skin because humans have salty skin.
The dogs usually love the taste of that salty skin and are licking your skin to remove that salt because they love the taste.
The dog could also be licking you as a sign of affection and showing it's love for you and wants to be loved back.
Licking humans also gives the dog comfort and pleasure but most commonly it's due to the salt on your skin.
If you ever lick your own skin especially when you're sweating you'll usually get a salty taste and that's what the dog is usually after as the dog may also have a salt deficiency and is licking you to increase it's salt intake.