Theory:

Everyone knows how the vowel O sounds, right?

O as in DOG.

But what about O as in SOME?

Or O as in NO.

Or O as in Lose.

Or O as in sailOr.

The vowel O has at least 5 different sounds, and that is why spoken English can be complicated to understand, and speak.

It is impossible to look at the letters of any word and predict how the word should sound.

The only way to pronounce a word correctly is to learn the sound of each word individually.

So let's start wit the letter O.

There are many words where the O sounds like the U in cUp, and here are some of them:

SOME

COME

MONEY

HONEY

MONDAY

MOTHER

BROTHER

MONKEY

OTHER

COMFORTABLE

WONDERFUL

GOVERNMENT

Another very common sound for O is like the O in nO. This sound needs a bit of practice: the sound starts at O as in DOG, and changes to U as in YOU, O > U.

Common words with this sound are:

NO

GO

COLD

PHONE

GOLD

HOLD

TOLD

In fact any word which finishes with the silent E, as in nosE, will have this O sound.

The normal sound for O as in dOg is also very common:

GOT

DOG

HOT

KNOT

POT

This is the sound when the word doesn't finish with the silent E.

There are some words, not many, where the O sounds like the O in lOse:

LOSER

WHO

WHOSE

TWO

THROUGH

Then, in words where the O is not part of the dominant syllable, the O sounds like the aah of Schwa, as in sailOr:

ACTOR

MAJOR

MOTOR

Often the same word may have two O's, and both sound differently, as in MOTOR.