HIRE DOCTORS: Tap on the button on the bottom right part of the screen, make an offer to any of the doctors available for hiring (you can swipe to the right to see more candidates). Keep an eye on the doctors' attributes to hire the proper one for each department! 
 
*You can also hire special doctors by spending gems at the shop! Tap on the STORE button if you want to get the best doctors in town!
 
 
ASSIGN A DOCTOR TO AN OFFICE: Once you have a new room built, tap on it to open the specific room menu. Then select the "Personnel" tab to find all your doctors already hired. Once you find the proper one for your new office (remember that they may have some useful attributes), tap on the ASSIGN button.
 
 
REPLACE AND FIRE DOCTORS: As you gain prestige in your hospital, some of the doctors may need to be replaced, or even fired! Tap on the button on the bottom right part of the screen to manage your staff. Select a specific doctor assigned to an office to replace him/her. If you want to fire a doctor, take in mind that he/she must need to be not assigned to any room. You should first replace him/her and then tap on "FIRE".
 
Remember that you can negotiate their salary according to your financial possibilities, but if their salary would be too low, they will probably refuse your offer.