that

Introducing a clause that is the object of a verb, especially a reporting verb or verb expressing belief, knowledge, perception, etc.

He told me that the book is a good read.

I believe that it is true.

Introducing a clause that is the subject of a verb, especially the 'be' verb or a verb expressing judgement, opinion, etc.

It is almost certain that she will come.

It amazes me that people still believe this nonsense.

Introducing a clause that is the subject of a verb, especially the 'be' verb or a verb expressing judgement, opinion, etc.

That she will come is almost certain.

That people still believe this nonsense amazes me.

Introducing a clause that complements an adjective or passive participle.

I'm sure that you are right.

She is convinced that he is British.

Introducing a clause that complements an adjective or passive participle.

Be glad that you have enough to eat.

The (thing, person, idea, etc) indicated or understood from context, especially if more remote physically, temporally or mentally than one designated as "this", or if expressing distinction.

That book is a good read. This one isn't.

That battle was in 1450.

The thing, person, idea, quality, event, action, or time indicated or understood from context, especially if more remote geographically, temporally or mentally than one designated as "this", or if expressing distinction.

That's my car over there.

He went home, and after that I never saw him again.

The thing, person, idea, quality, event, action, or time indicated or understood from context, especially if more remote geographically, temporally or mentally than one designated as "this", or if expressing distinction.

They're getting divorced. What do you think about that?

They gave me the book about whales. That I've not yet read.

The thing, person, idea, quality, event, action, or time indicated or understood from context, especially if more remote geographically, temporally or mentally than one designated as "this", or if expressing distinction.

The water is so cold! — That it is.

Would you like another piece of cake? — That I would!

In a relative clause, referring to a previously mentioned noun, as subject, direct object, indirect object, or object of a preposition; which, who.

I didn't see the car that hit me.

The CPR course that she took really came in handy.

Used in place of relative adverbs such as where or when; often omitted.

the place that [= where or to which] I went last year

the last time that [= when] I went to Europe