The glottis and velar port are closed, so that no air flows into or out of the lungs or nasal cavity. Then a stop-like occlusion is made. Pressure behind the stop closure is raised by raising the glottis, so that when the stop is released, there is a little plosive burst. Then the glottal stop is released. Hausa is the principal language of Northern Nigeria.
Ejective fricatives are possible too, though considerably more rare.
You can find several examples in the Sounds of the World's Languages database. This is used in all stops we have looked at so far. An alternative is to reduce the pressure in the sealed cavity, so that there is a little implosion when it is released. This can be done with glotallic sounds, and it requires the speaker to lower the glottis once the velum and oral cavity have been sealed off. This usually causes some air to move between the vocal folds, and so these sounds are voiced.