Singular means one (1).

Pronouns Be

1. I am early.
2. You are early.
3. She is early.
4. He is early.
5. It is early.

I, you, she, he and it refer to one person.

Pronouns refer to nouns.  (people, places, things and ideas)

Am, is and are = a form of the verb be.

6. Diana is early.  > She is early. 

She is used for women and refers to Diana. 

7. John is early. > He is early. 

He is used for men and refers to John.

8. Bus 24 is late. > It is late. 

It is used for women and refers to the bus.