Uses of that

That can be used as an adjective and a pronoun. It is the singular form of those.
Compare:

• Look at that man over there.
• Look at those men over there.

As an adjective that can refer to either people or things.

• This photograph is much better than that photograph.
• That boy says that he is tired.

When that is used as a pronoun without a noun, it can only refer to things.
Compare:

• Look at that photograph. OR Look at that.
• Ask that man to come here. BUT NOT Ask that to come here.

However, that can be used as a pronoun when we are identifying people.

• Who’s that?
• Is that Ruth?

In a colloquial style, that can be used as an adverb.

• I couldn’t walk that far. (= I couldn’t walk as far as that.)

Relative pronoun
That can be used as a relative pronoun. As a relative pronoun, that can refer to both people and things.

• The letter that came this morning is from my brother.
• Give help to anyone that needs it.

That as a conjunction
That can also be used as a conjunction.

• His manners are so bad that nobody invites him to a party.
• Bring it to the light so that I can see it better.
• You may borrow my car on condition that you bring it before 10 pm.

That can also be used in exclamations.

• Oh, that I could see you again! (= How I wish it were possible for us to meet again!)

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