As you advance in the game, you will be able to recruit skillful employees to your barbershop! The game will give you the opportunity of unlocking the first one, but you can unlock more characters using gems. The system will provide a card randomly, so you can receive a new heart for one specific character already unlocked, OR unlock a new character. 
Each character will have a special booster that will be applied to your earnings. The more cards you get from a specific character, the higher booster you will have, and the more hearts will be added to this specific character's counter. Moreover, your workers will have their own story! Unlock their chapters by meeting the requirements displayed in their descriptions (Working team's icon, over the yellow shopping cart button, lower-left side of the screen).
If you want to change your working team, you only need to tap on the staff button (over the yellow shopping cart button). There you will see all the characters available and the boosters they will apply to your barbershop while they are working there.