To make the /ɑʊ/ sound: /ɑʊ/ is a diphthong, which is like a combination of two different vowel sounds. To begin, place your tongue low in your mouth, and shifted toward the back, to say /ɑ/. Then, as you vibrate your vocal cords, lift your tongue high in the mouth, but keep it shifted toward the back, to say /ʊ/. The transition between these two positions should be very quick.