Translation:It is nine o'clock.
the word o' is a preposition used to represent the word "of" usually used directly before another word, such as in "a bottle o'beer" or "land o' lakes".
O'clock is a combination of two separate words to mean "of clock", or more directly, from the clock.
I would say that duo means to emphasize that there are definitely two separate words like in the combination of "y'all" (you all).
In learning language it's important to understand how a combination word was put together for a better understanding on how to flex its usage in different scenarios.
For more wordy lecture lecture lecture on something as simple as this...visit
Which example are you talking about? です has to be translated to the verb "be" and you need to add back the subject in English when the Japanese sentence doesn't have one. So the answer has to include "it is" (because it doesn't make sense to say "I am," "you are" etc. in this sentence).