This consonant ng' is one sound consonant, just a different sound of "n" (nasal velar, /ŋ/) as in English "sing", and the second sound is a prenasalized "b" with two sounds (m+be). The stress is on the first syllable ng'o.
Here some pronunciations:
https://www.youtube.com/watch?v=BntsggNJt28 (Learn Swahili Try 1/2)
https://www.youtube.com/watch?v=t9rIE8jdJuQ (Learn Swahili Try 2/2)
From Wikipedia: https://en.wikipedia.org/wiki/Velar_nasal