There is a trick to pronouncing words with the letter z. The trick is that the tip of your tongue doesn’t touch the roof of your mouth.

zoo
[z/oo]

 

 

This sound can also be made by the letter s.

position                                                         visible                                                         visit
[poh/zih/shun]                                                [vih/zih/b’l]                                                   [vih/zih/t]