what, watt

What or what is a pronoun--a sort of replacement for a  thing, person, place or idea--
What did you buy at the store?
What is the name of that song?
What is your name?
What is used to ask several kinds of questions--
"Oh, dear, what can the matter be?"
What is wrong?
What were you thinking?
What if we order 2 pizzas?

Watt or watt means a measure of power,  as a measure of electrical power, like the different kinds of light bulbs--the higher the watts on the bulb, the brighter it is, and the more electricity it uses--
The hundred watt bulbs make the room too bright.
You can save money on your electric bill by using 60 watt bulbs.

Note--"Watts" refers to a section of the city of Los Angeles, California--
The Watts Towers are a famous landmark.
Not to be confused with "watts", meaning a measure of power--
This light bulb says 60 watts.
Note # 2--"what's" is a contraction ( short, informal form ) of "what is"--
What's the matter?
"What's up, Doc?"