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Meanings:

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The Letter “A” does not have any sort of intrinsic “meaning” in the mundane sense.  Instead, it has various different “functions” — as both a Grammatical Unit, and an Element OF a Grammatical Unit.  Though it does not have a Meaning — The Letter “A” DOES — however — have many different Usages.
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Usages:

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1.  The First Letter Of The English Alphabet  —  Read The Full Post Here
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2.  A Grammatical Unit Referred To As “The Indefinite Article” — referring, non-specifically, to one of some “thing”, and appearing before Nouns (or the Adjective(s)/Adjectival-Phrase(s) that describe that Noun).
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• The Article “A” appears before words that start with a Consonant, and — in The Common Tongue — also appears before words that start with Vowels that have an almost “Consonant” affect.  Such as The Letter “Y” when it is used as a Consonant, and The Letter “U” when it is pronounced with a Consonant “Y”/Long “U” Diphthong — such as with the word, “University”.
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• Further-more — The Article “A” — in The Common Tongue — IS used in front of words starting with The Letter “H”.  This is because the breathy sound of The Letter “H” acts as a Consonant-sound — un-like in British-English (and also literary & scientific English) where-in it is more common to see The Indefinite Article “An” appearing before words that start with The Letter “H”.  This is because in British-English (and it’s related off-shoots — The Letter “H” is NOT usually pronounced at all…  Silly Brits!  :D)  This only continues today out of a matter of tradition and the personal whims of the speaker.
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• Finally — The Article “A” does NOT appear before Acronyms that may start with a Letter which is a Consonant when the pronunciation of that Consonant starts with a vowel-sound.  For example:  The Letter “F” (pronounced:  “ehf”)
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“An FBI agent should never simply be trusted.  One should always have a lawyer present when speaking to them or any law official.”

“I say A UFO on my first night in California.”

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In the first example above — The Article “A” is NOT used because the pronunciation of the name of The Letter “F” starts with the sound of The Short Letter “E”.
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In the second example above — The Article “A” IS used because the “U” of UFO is pronounced like the pronoun “You” — with The Letter “Y” taking the consonant sound.

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~ “The Teacher”

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Pronunciation Portal

• Learn The Pronunciation Of The Letter “A” Here
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Blog Portal

• Learn The Pronunciation Of The Letter “A”
• The Long “A” Pronunciation Like You’ve Never Heard It Before
• The Letter “A” — Grammar Lesson
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Other Sources

• Learn About The Letter “A” On Wiktionary

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