Go back to Nicholas's IPA Machine 
h
The letter h is usually pronounced in English.
There are only four words (or maybe five in America) that start with a silent h:
hour, honour, honest and heir. Because we don't say the h, we write "an" and not "a" before these nouns, so it's "an honour", not "a honour".
In British English we write "a herb" and "a herbivore", but many Americans also say herb with a silent h, so in American English these words can be written "an herb" and "an herbivore". There are twice as many hits on Google for "a herbivore", though, and the internet has more American than British websites.
Words with the IPA h sound
hi, hey, hello (or hallo), hotel, hat, him, his, hope, horse, heart, has, hazard, help
behind, Yahoo, prohibit, megahertz, coherent, beehive, treehouse, prehistoric
Words that start with a silent h
hour, honour, honest, heir
Words that contain a silent h
why, which, when, where, what, whatever, while, white, whisper, whistle, whisky, wharf, wherry,
vehicle, exhaust, rehabilitate, shepherd, hedgehog, posthumous, vehement, nihilist, annihilate
(and some recent French loanwords such as silhouette)
Words with a surprise h sound
who, whom, whoever