These are the 3 separate letters. Separate letters like these in combinations of 1, 3, 5 etc. can be found in many surahs of the Quran.
Educational Background of Prophet Muhammad (sallallahu alaihi wasallam):
Prophet Muhammad (sallallahu alaihi wasallam) was unlettered i.e. he had no background in formal education, and he was delivering Khutbahs to Muslims. On the other hand the ones delivering Khutbah to Jews (on Saturday) and Christians (on Sunday) were scholars. So, they would mock and insult the Muslims for this.
The Unconventional Recitation of Prophet Muhammad (sallallahu alaihi wasallam):
When Prophet Muhammad (sallallahu alaihi wasallam) would recite these letters separately instead of maybe saying “alam”, it would mean that Prophet Muhammad (sallallahu alaihi wasallam) was learning to read. That would send shockwaves to everyone (especially the Jews and Christians) because it meant he has a teacher. They wondered who the teacher was. It’s answered later that the teacher is Allah (subhanahu wa ta’ala).
Language Understanding at the Time of Prophet Muhammad (sallallahu alaihi wasallam):
At the time of Prophet Muhammad (sallallahu alaihi wasallam), when the Quran was recited everybody understood it irrespective of religion, because everyone knew the language.
The Arabs were very proud of their language. They thought of everyone else as less because they didn’t know Al-Arabiyya.
Unprecedented Nature of Quranic Verses:
Most of the poetry that is written is usually based on previous poetry. It draws inspiration from previous works. But when Prophet Muhammad (sallallahu alaihi wasallam) recites “Alif-Laaam-Meeem”, it was something like they never heard before. So, their mind is already getting prepared to accept revelation.
Meaning of Ayat #1
The position of Muslims is that only Allah (subhanahu wa ta’ala) knows what they mean.
All other meanings that exist of this verse and verses like these are only speculative.
It is wrong to say that it does not mean anything because everything that Allah (subhanahu wa ta’ala) says has meaning.
But why does Allah (subhanahu wa ta’ala) begin with words that we don’t understand?
In Surah Fatiha, we asked Allah (subhanahu wa ta’ala) for guidance. Surah Baqarah is the first response to this request (in the order of Mushaf). Interestingly, it begins with words that we don’t understand. This is for us to have the right attitude – an attitude of intellectual humility i.e. an attitude where we shouldn’t expect that we know everything. The attitude to bring to this book is not to critique or pass judgements if we do not understand. Instead, we should have the attitude that we don’t know anything and only Allah (subhanahu wa ta’ala) knows. The attitude to bring is that of a beggar, or the one who is lost in the desert and is desperate for water. Our attitude will determine if the Quran becomes a source of guidance or a source of misguidance. So, this verse actually puts a human being in its place.
Over and over when separate letters like these appear in the Quran, the next ayat is about the Quran.
By using different letter combinations, Allah (subhanahu wa ta’ala) tests us if we would get lost in the curiosity of these letters, or will we actually go ahead to achieve the purpose from this book.