Hi Friends

I am in little confusion.

All you are aware that 'a' should be used with words whose sound starts with constant and 'an' should be used with words whose sound starts with vowels.

But my doubt is when we say word constant or vowel,does it mean with any word we can use 'a' or 'an', or particular part of speech like verb or noun or adverb or adjective...?

If you guys can guide!
Thanks

There is never a Definite or Indefinite article before a verb.

Adjectives:
an eligible bachelor
an everyday occurrence
a good-looking stranger

Adverbs:
a very silly remark
an eagerly awaited phone call
an oft-quoted saying

Nouns:
an eagle nested on the cliff face
a case of apples