There are a number of ways to add emphasis to your sentences in English. Use these forms to emphasize your statements when you are expressing your opinions, disagreeing, making strong suggestions, expressing annoyance, etc.
Cleft sentences: It is/ It was
Sentences introduced by ‘It is’ or ‘It was’ are often used to emphasize a specific subject or object. The introductory clause is then followed by a relative pronoun.
It was I who received the promotion. It is the awful weather that drives him crazy.
Cleft Sentences: What
Sentences introduced by a clause beginning with ‘What’ are also used to emphasize a specific subject or object. The clause introduced by ‘What’ is employed as the subject of the sentence as is followed by the verb ‘to be’.
What we need is a good long shower. What he thinks isn’t necessarily true.
Exceptional Use of ‘Do’ or ‘Did’
You have probably learned that the auxiliary verbs ‘do’ and ‘did’ are not used in positive sentences – for example: He went to the store. NOT He did go to the store. However, in order to emphasize something we feel strongly these auxiliary verbs can be used as an exception to the rule.
No that’s not true. John did speak to Mary. I do believe that you should think twice about this situation.
Note this form is often used to express something contrary to what another person believes.
Let’s focus on cleft sentences especially since this is a new grammar point you’ve never come across before.