There are multiple sounds using the letter O. In most cases, you make this
sound with the rear portion of the mouth. You start with your mouth in an open
state. Your tongue should also be away from the top part of the mouth. Then you
make the sound by bringing in the lips in a circular manner and the tongue
moving upward and towards the front of the mouth ending right in the middle.
If you combine the "oh" and "oo" sound, you have the sound
of the letter "O". Along with these sounds, it is common to use
"O" with other vowels such as "OU" as in Hour. We will see
examples for all these types below.