We use cleft sentences to emphasise different parts of the sentence, they usually begin with it or by a clause beginning with what.
‘It’ Cleft sentences.
A simple sentence might be:
You spoke to the manager on the weekend.
We can add emphasis by moving the information we want to emphasise to the front of the sentence and adding it + be.
It was you who spoke to the manager on the weekend.
Emphasis: you (not another person)
It was on the weekend that you spoke to the manager.
Emphasis: on the weekend (not another time)
It was the manager that you spoke to on the weekend.
Emphasis: the manager (not another person)
”What” cleft sentences
What, where, why, who, how, clauses + be emphasise the part of the sentence that is outside the clause. This clause can be at the beginning or end of the sentence.
What I hate is when people use their phones while driving.
How they will adapt is not yet known.
The food at the Chinese restaurant was what I liked the most.