While the English language is characterized by a very strong glottal stop, the German glottal stop is much softer.
In German you should use a glottal stop when words are beginning with a vowel.
In a very correct and formal speech every word with a vowel in an initial position starts with a glottal stop. If you are not an English native speaker, but a speaker of other languages like Spanish or Italian, for example, maybe you don't have any idea what that means: the glottal stop.
We'll try to describe it: Deep in your throat you have to close the vocal chords for a short moment and you start your vowel with a little kick. It's as if you would like to clear your throat - but without your voice. If you try it out we are quite sure that you'll find it terrible. This means that you are overdoing the exercise - and that the position of your occlusion is perhaps too deep in your throat. Lift it up. And do it very softly, so softly that you practically can't hear it.
We'll try to give you an example. Click on the audio file and you can listen to an isolated, voiceless glottal stop. But it's exaggerated because otherwise you couldn't be able to hear it. It can hurt when you perform it in this exaggerated way and it's not good for your voice. You can soften it, when the impulse comes from your diaphragm. Listen, you can hear it three times (we turned up the volume):