The sound /h/...
... is the air coming out of your mouth
... is always followed by a vowel sound
As you say /h/, your tongue & lips shape the vowel sound that follows.
|h||at beginning of a word|
|silent w||who whom whose||unstressed h||Oprah exhibition Graham
linking "him, her"
|gh = /g/|
|rh = /r/|
|th = /t/|