A cleft sentence is used to add emphasis to what the speaker wants to say. This emphasis is created by adding certain phrases or words at the beginning of the sentence. (INTRO: page 95 of Cambridge advanced English textbook: Speaking activity 4:)
Here is a list of the most common types of cleft sentences…
1. What (synonym = the thing)
What I really want is a new car.
What I’m thinking is bad…very bad.
What I like is ice cream.
2. All (synonym = the only thing)
All I want is to be left in peace.
All he paid was 20 Euros.
All he did was say ‘hello’ and leave.
3. What happens is / what happened was
This type of cleft is used to empasize a series of events or a sequence or an individual event.
What happens is that you pay and then you enter.
What happened is that he shouted and then Ariana waved back.
What happened is a mystery.
4. The guy who / The thing which / The place where / The reason why etc.
The guy who did it was tall and fat.
The place I stayed in was 50 bucks more expensive.
The reason I wanted to go was the golf courses.
It wasn’t me who did it.
It was that guy who didn’t wash his plate.
It was the salmon that cost extra.
Note that unlike Spanish and other languages, you use the object pronoun after it is / was etc. This means you say ‘it was me’ rather than ‘it was I’.