The “H” sound denoted by the letter aitch is called a glottal fricative sound and is made by breathing out through a slightly narrowed opening at the very back of your mouth and the top of your throat. This is achieved by slightly closing up your airway so that the air hisses slightly: “HHH”. If you yawn your throat open, and breathe out then the flow of air should b almost silent. Experiment by breathing out through your mouth silently and then making this slight change so that you can hear the “HHH” sound. The name of the letter H is often mispronounced as “haitch” by many native British speakers - this is understandable but, perhaps counterintuitively, the name of this letter doesn’t contain the “HHH” sound that it represents. However, English is “a living language” so if enough people say haitch then it could become what’s called “an acceptable variant” - but I hope not!
Sometimes the letter H is silent as in
But, as ever, consult your trusty dictionary to double check any confusing pronunciation problems!