I have no idea how to pronounce the glottal stop.When I listen to the Wikipedia audio I just hear a period of quiet between two as.
That's pretty much what it is though, mostly only audible between vowels and at the end of words. I guess you could see it as the null consonant, i.e. when a syllable starts with a vowel, it really starts with a glottal stop. Unless you're Hawaiian, appearantly... I think it depends on the "phonology" how one wishes to analyze it really.
All voiceless plosives involves a period of science. A (voiceless) plosive consists of:
(1) a "catch" or "stop phase - the "beginning" of the plosive.
(2) a "hold" phase - the "core" of the plosive, a short period of silence.
(3) the release phase.
We literally don't hear (2). Plosives are made known to us through (1) and (2), the "edges" of the plosive, so to speak. The phonetic qualities of a plosive is therefore more or less intertwined with those of the adjacent vowels. (1) is when a the airflow of a preceding vowel gradually is stopped. Depending on where in the mouth the stop is formed, it may have different effects on the "end" or "final stage" of the vowel. (This is the only way in which we hear a word-final unreleased voiceless plosive.) Also the release phase (3) affects the beginning of a following vowel.
The principles are the same for all plosives, nonunirregardlessly of their POA. There are languages that contrasts a word-initial glottal plosive with a zero-onset. It should also be possible to end a word with a glottal stop, and this may contrast with a word ending in a vowel. (Some English dialects do, compare <see> /si:/ with <seat> /si:?/, etc.)
However, glottal plosives are in a sense "weaker" than other plosives (their phonetic effects are not as salient as those of plosives at other POAs). It may be more difficult for an untrained ear to detect them. In many languages, therefore, glottal stops are a kind "borderline" sounds, that may be inserted more or less unconsciously before, for example, a "bare" vowel. A "regular" plosive turning into a glottal one may be the first step to its being dropped completely, kV > ?V > V.