I guess my best advice is it's the same kind of muscles used as when you force a cough. When you cough, you fully block off the airflow and release it in a quick burst, but when you make the ע sound, you only reduce it and let the air stream through for a while. So do the first part of forcing a cough, the part which is like holding your breath, and then let out a bit of air but keep the tension. And it's voiced of course.
- Standard Hebrew: [ʕ] https://en.m.wikipedia.org/wiki/Voiced_pharyngeal_fricative
- Modern Hebrew: [ʔ] https://en.m.wikipedia.org/wiki/Glottal_stop
The glottal stop can be heard between the two vowels in the English "uh-oh!": [ˈʌʔoʊ].