The underlying reason of your confusion, I believe, is that there is no consistent vowel sound that can be heard across all of the world's English dialects (or even just the major ones) that is closely equivalent to the Lojban "o". All the English vowels near "o" tend to be weird in one way or another, varying, merging, diphthongizing, etc. So Lojban guide authors are naturally and understandably hesitant to give a precise "this is it" definition for "o" to English speakers.
If you know any Spanish, then Spanish "o" is fine. If you know the two Italian "o" sounds, or the two (Parisian) French ones, or the two (Standard) German ones, aim for the middle of any of those pairs. These are close; Japanese "o" is also close. Lojban's "o" is actually more international than English's approximations.
As a northeast American English speaker myself, I would say if you know how northeast Americans tend to pronounce the "o" in "coffee" (AW not AH), then say that vowel, but make it nice and "round" with the lips. Otherwise, say a long-o sound as in "boat" and try to drop the useless "w" sound at the end of that sound. That's tricky; you will need pay attention to your natural tendencies. With practice, it's doable.