ㅗ and ㅜ are not a korean letter for a "w" sound.</pre>
ㅗ sounds like the English word "Oh". ㅜ like the vowel sound in a cow's "moo". ㅡ like a shorter vowel sound in "look". The w sound happens when ㅗ or ㅡ or ㅜ are combined with other Korean vowels.
의 와 위 외 are examples.
The Romanization, using English letters, cannot give the true sound of the Korean letters. But, it is used to help students using books when no audio is available.
We will need to repeat lessons until we learn to think the Korean sound when we see the Korean letters.*
Until the tips and notes are put into the mobile apps, I sign into Duolingo on the web to read them for the Alphabet lessons.
*I hope in future versions of Korean for English speakers, there will be a way to start using only the 한극 alphabet audio with words like spell, translate, from and alphabet.