Here is the list of the sounds that the vowel o and combinations with o have in a stressed syllable.
Long /uː/ and short /ʊ/: a spoon for the cook
The combination oo makes a long or a short u sound. Of course, you can get these sounds with other combinations as well.
choose, food, spoon, proof, school, group, two
cook, book, shook, took, would, could, woman
Long sounds /ɔː/ and /ɜː/: a short word
The combination of or, ou, our often sounds like a long o. Note that if the word starts with wor-, or is pronounced as /ɜː/. However, it isn't always so.
corn, more, short, horse, brought, fought, four, mourne
worse, work, world, word, worship
Long sounds /əʊ/ and /aʊ/: at home now
In the pattern O_consonant_E, in some words with a single stressed o, in the combinations ol, oa, ow the letter "o" is sometimes pronounced /əʊ/.
The combinations ou, ow can also produce the /aʊ/ sound.
alone, code, episode, home, joke, note, phone, pole, role, stone, those, vote
ago, go, no, so, both, local, October, over, won't
control, gold, old, sold, soldier, told
boat, coast, goal, load, toast
below, bowl, flow, know, slow, snow, throw
about, cloud, discount, house, loud, mouth, pound, shout
allow, brown, crown, how, powder, towel
Short sounds /ʌ/ and /ɒ/: come, dog!
The letter o can give a short sound which is either closer to "a" — /ʌ/ or to "o" — /ɒ/.
come, month, colour, front, mother
dog, comedy, box, song, coffee, copy, cost
Long sound /ɔɪ/: a boy has a toy
The combinations of oy and oi are often pronounced /ɔɪ/.
boy, toy, enjoy, point, join, moist