English does not have any complicated grammatical gender system. People are usually he or she. Things are it.
- He is a teacher. (NOT It is a teacher.)
- She is a doctor.
- It is an apple tree. (NOT She is an apple tree.)
Sometimes he and she are used to refer to animals. This usually happens when they are being thought of as having personality.
- I have a rabbit called Joe. He is very cute. (More natural than ‘It is very cute’)
Some people use she for cars, ships and bikes.
- The ship has struck an iceberg. She is sinking. (OR It is sinking.)
Cases where the sex of a person is not known
English has traditionally used he in cases where the sex of a person is not known.
- A teacher can’t do a good job if he doesn’t have patience.
Nowadays this usage is regarded as sexist. Instead, may people use the expression he or she.
- A teacher can’t do a good job if he or she doesn’t have patience.
In an informal style, they is often used instead of he or she.
- If anybody hasn’t registered yet, he or she should do so at once. (More formal)
- If anybody hasn’t registered yet, they should do so at once. (Informal)