Do Australians use a herb or an herb in sentences?

Answer 1

The rule used in all English is to use 'a' before a word beginning with a consonant sound, and 'an' before a word beginning with a vowel sound. Note: it is the sound of the word, not the spelling that is important: 'a apple' is not clear when voiced, so 'an apple' is used. Herb used to be pronounced 'erb', with a silent 'h', thus it would be 'an herb', when spoken it sounds like 'an erb'. 'a erb' is difficult to hear or say properly. In modern times, the 'h' is sounded, so 'a herb' is acceptable. That being said, those who prefer the correct English will still use "an" before some words beginning with 'h', such as "an historical occasion" but not "an holiday".

Simple answer: No. Australians say "a herb" not "an (silent h) herb" as the Americans do.