This sound is not pronunced using the tip of the tongue, as in a normal T. Rather, it is pronunced by suddenly closing your throught.

Glottal stop (especially used before a vowel, as in "water") is considered by many bad English or even a sign of a poor education, and there is no need to use it if you are not a native, but you will often have problems to understand native English people if you don't know that this sound exists. It is getting more a more common in colloquial British English. It is very common in some British dialects. It is quite common in Australia and New Zealand, and in one case (at the end of pronunciation or before consonants) it is very common all over the English speaking world, so get used to it!

Cases when you can't use a glotal T:

- When that T starts a word (e.g. tea, timing).

- When that T is in a stressed syllable (e.g. hotel, attack, student)

Cases when you rarely use a glotal T:

After some consontans, such as S or N (e.g. mountain)

Cases when you often use a glotal T (even in American English):

- When the T is at the end of the sentence or before pause (e.g. "I have a cat")

- When the T goes before a consonant (e.g. Patmos)