Personal pronouns can be singluar or plural. They can be the subjects or the objects of verbs.
Examples:
- I see them every day.
- He knows her.
- Look at me.
- Give us a present!
Use it to refer to a thing or an animal, and sometimes to a baby.
-Lovely baby! Is it a boy or a girl?
It is also used with time and weather:
-It's five o'clock.
-It's raining.