*a glottal stop is that kind of slight gagging (where your throat closes up for a moment) which occurs at the beginning of ejecting a very short (surprised?) "uh", or try to pronounce an exaggerated "g"
Thank you Alharacas for the substantial information!
By the way, I never heard about glottal stops until I started learning Arabic. I found out they exist in all the languages but in Arabic they are written.
How does that work in Farsi? Do they also have the hamza sign ?