What

What is either a determiner or pronoun. It is a wh- word used to refer to "things".

What is used to form wh- questions, wh- clauses, and exclamations. It does not change its form.

1. What refers to things

What asks about something:
Example: "What are you looking for?" "I'm looking for a pen."

Who asks about someone:
Example: "Who are you looking for?" "I'm looking for the manager."

Note: We can ask what about a person's job.
Example: "What was her first husband?" "He was a teacher."
But its meaning is different from:
"Who was her first husband?" "He was John Forbes, the son of a famous writer."
"What" asks about a person's job. Who asks about the person as a person.

2. What introducing wh- questions

What as a pronoun can be subject, object, or complement.
Subject: What happened?
Object: What are you doing?
Complement: What is your name?

Other examples:
"What would you like to drink?" "An orange juice, please."
"What is her job?" "She's a nurse".

Notes:
(1) See wh- question 10 about short questions such as "What for?".
(2) The simple question "What?" is a "rather impolite" request for repetition.

What as a determiner goes before a noun: what + noun
Examples:
"What time is it?" "It's ten past five."
"What job does he do?" "He's an electrician."
"What year were you born (in)?" "In 1997."

Note: When it is a determiner, what can ask about people as well as things. It often means "what kind of".
Examples:
What (kind of) painters do you admire most?
What (kind of) people visit this restaurant?

3. What introducing wh- clauses (= subordinate clauses)

3.1. What as a pronoun

Let's see some examples below:
We asked her what she wanted.
Why don't you say what you mean?
I don't remember what he looked like.

These are indirect questions.

(Talking about a holiday):
What I enjoyed most was swimming.
Did you? Well, the food was what I enjoyed most.

These are referring clauses.

3.2. What as a determiner: what + noun

Can you tell me what size* this t-shirt is?
I don't care what difficulties we face.

These are indirect questions.

They stole what money we had.
What supporters he had soon left him.

These are referring clauses.

(What money and what supporters here imply that the amount or quantity is small.)

* What size + noun is useful when we are talking about clothes.
"What size shoes/dress do you take?" "Size 6."

4. What introducing exclamations

4.1. What + a / an + singular countable noun

What a lovely dress!
What a beautiful day!
What a time we had! (= we had a very good time)

4.2. What + plural or uncountable noun

What strange neighbours you have!
What luck! (= good luck or bad luck)

I hope this article helps. If you have any question, please leave a comment in the comment section.