The “!” is used to signify a click.
With some languages we have problems because the sounds are neither vowel nor consonent. They are in fact nothing like anything produced in English. So representing them with vowels or consonants do not give an accurate representation, in fact they make the pronunciation worse. To deal with this we use non-English character representations for the non-English sounds.
In the case of the click languages like Xhosa and Kung, the sounds we can’t represent are clicks. Sounds similar to the “tsk tsk” sound of disapproval, or the sound made by bringing your tongue sharply down onto the floor of the mouth that people use when they want to mimic a horse trotting (and don’t have any coconuts).
By placing the “!” in front of a letter you indicate the precise type of click, and where it is made on the pallet. So “!K” is different from “!T”. But both are sounds of clicks. I won’t even pretend I know how to pronounce them though. The only person on the boards that I can think might know is Mr. Dibble, our resident Khoi San, so if I drop his name he might find the thread. Not sure if he speaks the lingo though.
But the simple answer is that it’s pronounced as a click/cluck, made with the tongue/pallet, not using the larynx at all. If you make the “horse trotting” sound I described above it will be at least approximately the sound intended.
Interesting sidenote: The “Kwa” in KwaZulu was originally a similar click sound. Because it was spelled with European characters most people never realised.