flew, flue, flu

Flew or flew ( pronounced "floo" ) is the past  ( yesterday, or some time ago ) tense of  the verb ( action word ) "fly"--
Yesterday a bird flew into the picture window. We'll have to keep the curtains closed.
He flew to New York last week on business.

Flu or flu ( rhymes with flew ) is a short form of "influenza", meaning a contagious disease something like a very severe cold--
Flu seems harmless, but it was a deadly epidemic during the First World War.
She can't go to work; she's still sick with the flu.

Flue or flue ( rhymes with flew )  means the opening in a chimney or boiler to let out the smoke or steam--
The house is full of smoke! You forgot to open the flue!
We can't light a fire, because the flue isn't working.

Now that you know that, you can say--
"He felt a chill because he had the flu, but when we closed the flue, bits of paper and ashes flew out of the chimney."

Note--"fluid" ( pronounced floo--id ) means liquid, or having some of the same properties as a liquid--
Water is a fluid, ice is a solid, but steam is a gas.
Note # 2--"fluent" ( pronounced floo-ent ) means able to speak well, or quickly and clearly--
He studied five years before he became fluent in Spanish.