A.     what is a general interrogative used for things:

What bird is that?      

What makes that noise?

What country do you come from?      

What did he say?

B.     what . . . for? means 'why?':

What did you do that for? = Why did you do that?

C.     what + be ... like? is a request for a description and can be used for things or people:

What was the exam like? ~ It was very difficult.

What was the weather like? ~ It was very windy.

What's the food like in your hostel? ~ It's quite good.

Used of people it may concern either appearance or character:

He's short and fat and wears glasses.

He's a very talkative, friendly man.

what does he/she/it look like? concerns appearance only, and can

also mean 'What does he/she/it resemble?':

What does she look like? ~ She is tall and glamorous. She looks like a film star.

What does it look like? ~ It's black and shiny. It looks like coal.

D.    what is he? means 'What is his profession?':

What is his father? ~ He is a tailor.

what (adjective) used for persons is not common: What students are you talking about? is possible, but Which students . . . ? would be much more usual.

E.     what and how in questions about measurements

We can use what + age/depth/height/length/width but in

conversation it would be more usual to say how old/deep/high/tall/

long/wide?

what size/weight? is usual when an exact answer is required,

though how big/heavy? is also possible.

What age are you?/What is your age?/How old are you?

What height is he?/What is his height?/How tall is he?

What is the weight of the parcel?/How heavy is it?

What size do you take in shoes?