"It" and its other forms "its", and "itself" only refer to objects, not people. "They" and its other forms "them", "their", and "theirs" can be used as a singular, for a person whose gender is unknown at the time, or for a person who does not identify with either the "she/her" or "he/him" pronouns. For example: "The patient will be told how much "they" will be required to pay." 