learning - "a" or "an" for words that don't start with vowels but sound like they're starting with a vowel

Is it correct to say or write an student or an store?

Answer

Always use an for words which sound like they start with a vowel, and always use a for words which sound like they start with a consonant. The rules for h are more complex, and it can be ok to use either.

The usage of the indefinite article preceding h are discussed here. In particular, look at nohat's response.

As for student and store, they should always be preceded with a and never with an, because they both start with the consonant /s/ when spoken.

Correct:

A student, a store

Incorrect:

An student, an store